The myology of the limbs of Pteropus.

THE MYOLOGY OF THE LIMBS OF PTEROPUS. By PROFESSOR HUMPHRY (Pl VI. & VII.) THE muscles of the limbs of Cheiroptera present so many features of interest that I think it worth while, although they have been described by others, to give an accurate description of them as recently dissected by me in two specimens of Pteropus Edwardsii, a male and a female. The peculiar features of interest are, first, the modifications by which the muscles of the fore limb are adapted for flying, leading us to observe by what slight deviations from the ordinary mammalian type the end has been attained. The large pectorals springing from a keeled sternum, and the tensores plice alaris constitute some approach to the peculiarities of the bird. The latter muscles, however, do not spring, as in the bird, from the shoulder girdle, but are obviously prolongations of the platysma, and no part of them passes to the forearm; nor does the deeper stratum of the pectorals (pect. min. and subelavius) show any special avian characters. Moreover the resistance to the pull of the pectoral muscle upon the shoulder is afforded not by the presence of a coracoid bone or by the union of the clavicles, but the manner in which the broad flat surfaces of the strong clavicles are jointed with corresponding articular surfaces on the sternum. The biceps has, in one of the specimens, a slight muscular slip from the humerus; but this is not uncommon in mammals or indeed in man, and it is rather a detachment from the brachialis anticus than a distinct origin of the muscle, as it is in the bird, from the upper end of the humerus; and unlike the same in the bird, the main (coracoid) portion of the muscle is in two parts, and these are unusually distinct. The supinator longus stops short at the upper third of the radius, acting simply as a flexor of the forearm; and the radial flexors and extensors of the carpus are inserted as in mammals, none of these muscles being attached, as their two representatives in birds are, to the foremost metacarpal. The flexor carpi ulna-is arises as usual. It does not, as in the THE MYOLOGY OF THE LIMBS OP PTEROPUS. bird, arise behind the inner condyle and pass beneath it, playing under it as under a pulley. This provision in the bird for harmonizing flexion of the carpus with flexion of the elbow, like the provisions in the supinator longus (its connection with the tensor plicae alaris above and with the metatarsus below) for harmonising extension of the carpus with extension of the elbow, is wanting in Pteropus. In these and in the other myological differences from birds we recognize an inferiority in the adaptation of the animal for flight which is more strongly evinced in the want of concentration and simplification of the osseous and muscular structures characterizing the distal segment of the bird's wing, and which is most of all shown in the dermal extension as a substitute for feathers, whereby the hinder limbs are involved in the work of aerial movement and are unfitted for any other mode of locomotion'. Thus, while we admire the manner in which this order (Cheiropterous) is specialized for flight from a class (Mammalian) which is not constructed for such movement, we are conscious of the great superiority of the mechanism attained in the several members of that class which is throughout, or in great measure, constructed for flight, and in which the hind limbs are left free to subserve to terrestrial locomotion, while better motor power in air is obtained by the more perfect adaptation of the fore limbs and of the body generally. A similar illustration of the same principle is found in the fact that the mammalian inhabitants of the deep show their adaptation to the watery medium to be inferior to that of the fish, by the necessity which compels them to come to the surface for the purpose of breathing air. Secondly. It is interesting to find that though the hind limbs are unfitted for the performance of the locomotory functions, they, nevertheless, retain in the main the structural composition and disposition of parts usual in those limbs. The functions of the hind limb in Cheiroptera are almost exclusively those ordinarily assigned to the fore limb; yet they are effected by a modification of the ordinary structure of the hind limb rather than by a substitution of that of the fore limb. The 1 The reduction of the number of the phalanges in the fore limb to two in each of the three ulnar digits has relation no doubt to their great length and attenuation, which is incompatible with the additional source of weakness that would have been entailed by the usual series of bones and joints. 295 PROFESSOR HUMPHRY. peculiarities, that is to say, of the hind limb, or most of them, are retained. The femur is jointed with one leg bone, although the rotary movement of the leg upon the thigh is lost. The tarsus is articulated with the tibia, by one bone-the astragalus-; the scaphoid intervenes between that bone and the distal row of tarsals, and the os calcis stands up towards the middle of the flexor aspect of the limb to receive the tendo Achillis. Some approximation, however, to the osseous conformation of the fore limb is found in the fact that the os calcis is situated chiefly on the fibular side of the ankle, rises to a level with the astragalus, and subtends the lower end of the fibula, reminding us of the relations of the cuneiform to the scapho-lunar and to the ulna. Moreover the small size of the tarsus in relation to that of the metatarsus and phalanges are reminders of the ordinary relations of the carpus to the metacarpus and digits; and the foot is in the same plane with the leg. With regard to the muscles, the gastrocnemius is derived from both the condyles, and the peroneus longus, in spite of the absence of the upper part of the fibula, is present, and takes its usual course; and the various muscles of the foot and leg present the usual characters of the hind limb, except that the flexors of the leg run all together to its middle instead of passing, in two divisions, to its more lateral aspects. Thirdly. There is, however, an assumption by the hind limb of one character of the fore limbs, which renders the anatomy of these animals peculiarly instructive and valuable in instituting a homological comparison between the two limbs. I mean the direction of the flexor and extensor surfaces of the limb, which, instead of being, as it usually is, in the thigh and leg at any rate, the reverse of that in the fore limb, is, in Cheiroptera, very nearly the same with that of the fore limb. Thus, the extensor surface of the thigh and leg and the prominence of the knee, like the extensor surface of the arm and forearm, and the prominence of the elbow, are directed backwards, and the hallux and tibial line, like the polled and radial line, are on the outer side. In another place (Essay on the Limbs of Vertebrate Animals) I have shown that the fore and hind limbs, in their primary transitory condition in the fetus and in their persistent con296 THE MYOLOGY OF THE LIMBS OF PTEkOPUS. dition in some of the lower animals, are, in this respect, alikeare both, that is, directed in the same manner. They are both projected at right angles and nearly straight, from the trunk with the dorsal or extensor surfaces superior, and the polled and hallux with the respective radial and tibial margins anterior; and the flexion at the elbow and knee, in both, takes place upwards, away, that is, from the abdominal aspect of the embryo. Thus far the correspondence between the two limbs is pretty exact; and if things remained in this position there would be little difficulty in pointing out the serial homological relations of the several parts. But, while the flexion at the elbow and knee takes place, a rotation is going on in the two limbs and in opposite directions. The elbow with the superior or extensor surface of the fore limb becomes turned backwards, and the knee with the superior or extensor surface of the hind limb is turned forwards. This causes the hallux, tibia, tibial condyle and side of the femur, that is, the line of the hind limb which was originally anterior, to be directed inwards, and the pollex, radius, radial condyle and side of the humerus, that is, the line of fore limb which was also originally anterior, to be directed outwards. Rather, I should say, with regard to the fore limb, this would have been the effect, but that a rotation in an opposite direction to that in the rest of the member takes place in the middle and distal segments (the forearm and hand). This causes the polled and lower part of the radius to be directed inwards while the upper part of the radius and the radial line of the upper part of the limb retain the direction outwards which I have indicated. This opposite rotation of the two limbs has, I need not say, proved a source of much perplexity in their comparison and led to many errors. In Cheiroptera the rotation of the hind limbs differs from that which usually takes place in those limbs, and corresponds with that which takes place in the fore limbs. The convexity of the knee and the extensor surface of the limb are directed backwards; and the hallux, tibia, and tibial line of the femur are directed outwards: they afford us, therefore, a peculiarly favourable opportunity for comparing the muscles in the two limbs, and for settling some of the disputed points. They show, for instance, unmistakeably, that the extensor muscles (triceps) 297 PROFESSOR HUMPHRY. on the arm correspond with the extensor muscles (quadriceps) on the thigh, and that the flexors in the two limbs are in similar corresponding relation. They give additional support to the view that the inner, or tibial, condyle of the femur corresponds with the outer, or radial, condyle of the humerus, that the tibial (usually inner, in these outer) trochanter of the femur and the muscles passing to it are homologous with the radial (outer) tubercle of the humerus and its muscles, and consequently, that the muscles on the outer surface of the scapula are, to some extent, homologous with those on the inner surface of the ilium. Still, the rotation of the hind limb being the reverse of that which is usual, has so far altered the parts from their ordinary disposition that it is not, in every instance, easy to refer a given muscle to its correspondent in the hind limb of other animals. It is scarcely necessary to add that caution is, therefore, needed in drawing inferences with regard to serial homologies with the fore limb. These animals show that the direction of the rotation in each limb has no close relation to the particular structure of the limb; for in them, the rotation of a fore limb is associated with the ordinary structure of a hind limb. We must, therefore, look to some other agency as the determining cause of the direction of the rotation. At present I can discern no other cause than that mysterious agency in development, whatever it is, which determines the general conformation and the detailed structure of a limb in accordance with the part it will have to play in the economy of the animal. Nor do I see that the illustrations thus furnished of the modification of one order in a class to suit, to some extent, the habits of another class and the modification of one pair of limbs to fulfil, to s6me extent, the ordinary functions of the other pair, aid us much in the elucidation of the great questions of the mode of derivation of species. In each instance the change seems to be wrought out suddenly and completely, per saltum as it were. At least the known connecting links between these aerial and the ordinary terrestrial mammals are too few to enable us to draw any definite inferences from them. Some of the points of interest which suggest themselves I will refer to in the course of the description. 298 THE MYOLOGY OF THE LIMBS OF PTEROPUS. CUTANEOUS M USCLES are disposed as follows. They are remarkable for their extent, their disposition, and their osseous connections. The Platysmc portion consists of four muscular bands (1, 2, 3, 4 in Pl. vi.), (1) arising from the side of the lower jaw, where some of the fibres are blended with those of the muscles of the angle of the mouth', and from the side of the head behind the lower jaw. It is the 'cervico-facien' of Cuvier and Laurillard2. (2) from the hinder part of the parietal crest, from the occipital crest, and slightly from the middle line beneath the latter covering, in part, the space usually occupied by the cervical portion of the trapezium. It is the 'dorso-occipitien' of Cuvier, who regards this as the main portion, the other three being accessories. (3) from the middle line of the lower part of the neck, in front of the trachea, where it is confluent with the corresponding muscle of the opposite side. (4) from the fore part of the keel of the sternum, superficial to the pectorals major. These several bands, distinct from one another at their origins, converge to the free edge of the humero-radial expansion of skin, along which they run, forming a narrow band (5) (corresponding with the tensor police alaris in the bird8) as far as the polled into the side of the phalanges of which it is inserted. In the middle of the edge of the wing-fold the muscular fibres are supplanted by a thin band of highly elastic tissue. This again, one-third from the polled, gives way to muscular fibres which, after about an inch, terminate in common tendon. Thus there is first muscle, then elastic tissue, then muscle, and, lastly, tendon. The muscle thus disposed serves to give tension to the fold of the wing, bends the forearm upon the arm and the polled upon the forearm, also abducts the polled and so may aid in separating the digits and expanding the wing, besides exerting some influence upon the humerus. 1 This reminds us of the corresponding part of the muscle in Orycteropus (Vol. ii. of this Journal, p. 293) which passes from the depressor anguli oris upon the arm and forearm. 2 Anatomie Compar6e, Planches. S This muscle in the bird is derived from the deltoid or pectoral or both. 299 PROFESSOR HUMPHRY. Another cutaneous muscle (cutaneo-pubic) arises from the fore part of the pelvis and radiates over the abdomen, the front of the pectoral muscle, and the shoulder. A lateral band, taking a direction different from the rest of the muscle, passes into the wing on the outer side of the thigh and leg, and runs quite to the edge of the wing. A third muscle (P1. Vi. F. C., femoro-cutaneous) arises from the lower part of the tibial (or outer) side of the shaft of the femur and passes forwards radiating over the back. A fourth (I. C., ischio-cutaneous) runs from the ischium, across the ischio-pedal fold of skin and the supplementary calcaneal bone, upon the dorsum of the foot. A fifth (C. C., coraco-cutaneous) arises from the coracoid in company with the biceps muscle, leaves the latter in the upper third of the arm, and runs through the brachio-crural flap of the wing to its lower edge'. Neither of these are mentioned or represented by C. and L. Other similar bands of muscle, parallel with this last, descend, at nearly regular intervals, through the brachio-crural wing-flap to its lower edge from near the arm and forearm, though they do not appear to have any direct connection with the arm or forearm; and there is a broad thin muscular sheet extending from the back of the thorax and abdomen, near the spine, into this flap, and sending off bands which radiate in various directions in the folds of the skin. MUSCLES OF THE FORE LIMB. Pectoral in three portions: (1) Sternal portion (Pect.), of great size and thickness, arises from the. side of the keel of the sternum and the sternal ends of the sternal ribs, slightly from the lateral portion of the 1 In Echidna setosa and in the Jerboa a thick band of muscular fibres arises from the anterior tubercle of the humerus, close to insertion of the pectoral muscle, and runs into the pannicle on the side of the abdomen. Part of the pannicle is also connected, in the Echidna, with the edge of the ulna; and in the Jerboa it is, as in Pteropus, attached to the face and side and back of the head, and by a distinct slip to the sternum. In it, as well as in Pteropus, the latissimus dorsi is nearly covered by this part of the pannicle, and is, as it were, stunted by it, being very small. In the Mole and the Rat, also, the pannicle is connected with the sternum, the humerus and the ulna. It is rarely, however, attached to the coracoid. Soo THE MYOLOGY OF THE LIMBS OF PTEROPUS. manubrium sterni but not at all from the clavicle, to the ridge on the outer side of the bicipital groove of the humerus. (2) Clavicular portion, from the deeper part of the inner third of the clavicle, lies beneath the preceding, and beneath the deltoid, and might perhaps be regarded as belonging to either. It is inserted into the upper part of the same ridge in close relation to the fibres of the pectoral and of the deltoid. It is the 'petit pectoral' of C. and L., but may, probably, be more correctly regarded as a part of the pect. major. It does not arise, in either of my specimens, as represented by Cuvier, from the rib, but is connected only with the clavicle. It has not the ordinary characters of the clavicular part of the pectoralis major; for this usually lies more superficially, and crosses in front of the rest of the muscle to a lower part of the pectoral crest of the humerus. (3) Abdominal portion arises from the pubes in company with the rectus abdominis, forming the outer part of the compound muscle, separates from it as it ascends to the ribs, passes beneath the sternal portion of the pectoral, between it and the biceps, to the upper and inner margin of the same ridge just beneath the preceding. It is called ' portion ventrale' by C. and L. It' might be said that the rectus divides as it ascends and thus forms its outer detachment. In many animals (Fawn, Pig, Calf) a portion of the pectoralis arises from the sheath of the rectus or the linea alba. In Batrachians it is, as in this instance, blended with the muscle itself. The relation of this portion (which may probably be regarded as therepresentative of the Pectoralis minor), and of the subelavius in Pteropus as well as of the scaleni, in some animals, to the rectus suggest these may all belong to one series or one muscular plane commencing at the pubes, terminating in the cervical vertebrae and diverging to the shoulder, sometimes continuous, but more commonly interrupted by one or more ribs'. 1 The Pyramidalis is large, has a broad origin from the front of the pubes, and covers a considerable portion of the lower and fore part of the abdomen. The fibres ascend with an inclination inwards, and are chiefly inserted into the linea alba. Some however run on to the sternum and adjacent cartilages of the ribs. In the female Pteropus, the Pyramidalis arises from the pubes on the side of the pubic gap, just in front of the rectus. The fibres pass obliquely inwards to the line alba. The lowest are almost transverse, parallel with and quite close to the symphysial ligament, so as completely to cover all the part above the ligament in the interval between the recti. The upper fibres are more oblique. Rectus is attached above to the ribs wide of the sternum, as high as the first rib, 301 PROFESSOR HUMPHRY. Meckel's (Vergleich. Anat. iII. 454) description of the relation of the pectoral with the rectus in Vespertilio corresponds with the above. This anatomist believes that in cases where the pectoralis minor appears to be absent it is really blended with the scalenus (s. 490) and says the same is also occasionally the case with the subelavius (s. 416). Subelavius (Subel.) is large. It passes from the under surface and anterior edge of the broad sternal portion of the first rib (the rectus abdominis is inserted into the posterior edge), along the lower surface of the clavicle, to be inserted beneath its outer part. It is inserted exclusively into the clavicle. Serratus magnus anticus is in two portions, as Meckel describes. The upper, thick and muscular, arises from the first rib behind the subclavius and beneath the tendinous insertion of the scalenus and also slightly from the second rib, and is inserted into the upper part of the hinder margin of the scapula, internal to the insertion of the levator scapulae, but not extending so far down the scapula as it does. It is quite distinct from the levator scapule in its whole extent. The lower portion is broader, arises from the eight ribs below the first and is inserted into the inferior margin of the scapula between the teres major and the subscapularis. It is nearly the same in the two-toed Anteater, but the lower portion is in it attached more to the angle and hinder margin of the scapula than in Pteropus and does not advance so far forward between the teres and subscapularis. This muscle undergoes subdivision in Birds, Reptiles and Amphibia, especially in the Frog, with varieties of insertion. Rudinger, Die Muekeln der vorderen Extremiatten der Reptilien und Vogel. is joined near its upper part by the pectoral as above stated, and descends behind the pyramidalis to the pubes. There are no tendinous intersections in it or in the pyramidalis. In the female the recti separate as they descend to the pubic bones, leaving the lower part of the abdomen uncovered by them. Obliquus Externus, indigitating above with serratus, forms a thin expansion, covering the rectus and pyramidalis. Below, in the male Pteropus, it has a free edge some distance above the pubes; and beneath this edge the large spermatic cord escapes, carrying with it some fibres of the muscle beneath, the obliquus externus, which form a crernaster and are disposed nearly transversely upon the cord. In the female, where the pubic bones are widely apart and connected by a fibrous band passing across in front of the vagina, the lower margin of the obl. ext. is less defined. Its expanded tendon passes to the pubes and to the symphysial band. The obliquus interns passes entirely behind the rectus, no part of its tendon going in front. At the lowest part of the abdomen it is very thin. 302 THE MYOLOGY OF THE LIMBS OF PTEROPUS. with the succeeding muscle to the base of the dorsum of the first phalanx of polled. The 'interosseal adductor' is the extensor of the third or terminal bone of the pollex. Extensor indices, beneath preceding, and in company with it to the terminal phalanx of index'. Thus each of the terminal phalanges of the digits is supplied with an extensor, though those of iv. and v. are devoid of flexors. The differences from the dorsal muscles of the human forearm and hand are in the insertion of the supinator and in the extensores pollicis. MUSCLES OF THE HIND-LIMB. Psoas parvus (Ps. p.), from the two or three lower dorsal and the three upper lumbar vertebrae, a small muscle. Its slender tendon is inserted into the outer extremity of the projecting spine of the pubes which overhangs the hip-joint2. Some of its fibres are continued on into the pectineus. Psoas magnus (Ps. in.), from the bodies of all the lumbar vertebrae, lying external to the preceding, as well as from the front of the ilium and the adjacent surface of the sacrum, passes beneath the overhanging pubic spine, external to and behind the hip, to the outer or tibial trochanter. Iliacus internus (Ii. i.), from the outer surface of the ilium close to the crest, has no further connection with the ilium, is distinct from the psoas, and passes beneath it to the outer surface of the femur quite beneath the tibial trochanter. It crosses external to the extensor cruris. Sartorius, not clearly distinguishable. Cuvier describes under this name some fibres passing from the ilium to the lateral part of the pannicle. Meckel says it is absent in cheiroptera. Pectineus (Pect.), a round muscle in its upper part, arises by a strong well-defended tendon from the most projecting point of the pubic crest just beneath the insertion of the psoas parvus, and from the tendon of that muscle. Becoming wider and flatter it crosses anterior and external to the psoas and iliacus, and is inserted, beneath the latter muscle, into the 1 Meckel does not mention this muscle, but describes the ext. dig. as passing to the four fingers. 2 The mistake in the Leqons respecting the absence of this muscle as well as of the psoas magnus and the iliacus is rectified in the Anatomie Comnparie, Planches of Cuvier and Laurillard. 309 310 PROFESSOR HUMPHRY. middle of the outer (tibial) side of the femur. It is the ' pectineus' of Cuvier and Meckel; still it is a question whether it may not be the adductor longus of which there is no other representative; or it may be the representative of both these muscles. Adductor brevis, from the outer surface of the pubes under cover of the gracilis, between it and the obturator externus, crosses the psoas to the fore and outer surface of the femur immediately in front of the insertion of the iliacus. Adductor magnus. There is a considerable mass of muscle, consisting of three or more parts, arising from the outer surface of the pubes and ischium, appearing superficially between the gracilis and the semi-tendinosus and semi-membranosus, and extending beneath the latter muscles to the middle line. It is inserted along the fore part of the femur from the outer, or tibial, trochanter three fourths down the bone. An upper portion, easily separated, may represent the Quadratus femoris, and another portion, separated in great measure from the rest by the sciatic nerve and the origins of the semi-tendinosus and semi-membranosus and connected with its fellow in the middle line and inserted lower and rather more on the fibular aspect of the femur than the remainder of the muscle, may possibly represent the Biceps which, owing to the absence of the fibula in the upper part of the leg, may have stopped short in the thigh and acquired an attachment to the femur'. Gluteus Maximus (GI.) arises, muscular, from the hinder margin of the crest of the ilium and from the sacral spines, and is inserted, tendinous, into the upper half of the inner, or fibular, side of the shaft of the femur between the adductor mass and the vastus externals which is here internal. Glutamus Medius arises from the outer and hinder surface of the ilium, under cover of the gluteus maximus and iliacus, and is inserted, tendinous, into the summit of the inner, or fibular, trochanter. There is no glutwacs minimus distinct from the medium. Obturator Externus (Obt. e.) is a large muscle arising from the whole of the exterior of the obturator ligament and the 1 Cuvier and Meckel mention only one adductor besides the pectineus and make no mention of a quadratus. THE MYOLOGY OF THE LIMBS OF PTEROPUS. surrounding margin of bone. It passes immediately over the front of the hip-joint and is inserted into the outer part of the tibial trochanter and into the adjacent part of the capsule of the hip. It reminds one strongly of the supra-spinatus. Gernelli. A small short muscle arises from the deeper part of the tuber ischii near to and in front of the acetabulum and immediately in front of the preceding muscle. It is inserted into the inner surface of the inner or fibular trochanter. This I conclude may be regarded as the representative of the gemelli. None of its fibres entered into the pelvis. There is no trace of a distinct obturator interns either in the interior or on the exterior of the pelvis. Three flexor muscles of the knee pass from the fore and inner part of the pelvis to the middle of the plantar or anterior surface of the tibia, instead of being attached as usual to the sides of the leg, bones; in this respect resembling the flexors of the forearm. They are the three following. Gracilis (Gr.) from the edge of the spine of the pubes, in its whole length, also from the symphysis and from the rounded angle between the two. Its tendon joins that of the following muscle; Seemi-tendinosus from almost the hindmost part of the ischium (the back part of the tuber ischii). The tendons of these two are united in the lower third of the thigh, and are inserted into a projecting ridge in the middle of the back of the tibia, .Ith from the upper end, beneath therefore the space that would usually be occupied by the popliteus. Semi-menbranosua from the tuber ischii just in front of the preceding. Its tendon runs clear of the other two and above them to the same ridge a little higher up. This accords with the description of the above three flexors by Cuvier and Meckel, neither of whom admit the presence of the Biceps in Cheiroptera. The tendons of all these three lie entirely on the tibial side of the gastrocnemius which indicates them to be tibial muscles. The insertion of these flexors into the middle of the front of the tibia, instead of on either side of the leg bones, accords with the fact that, owing to the transversely excavated or grooved condition of the upper surface of the tibia, no rotatory motion-no pronation and supination-of leg can be effected. These movements are limited to flexion and extension as in the case of the two bones of the forearm upon the humerus; and the disposition of the flexor 311 PROFESSOR HUMPHRY. muscles is accordingly the same. It is also interesting to observe that there are no interarticular cartilages in the knee-joint. Extensor cruris (Ext. cr.), not large, from the margin of the ilium, external to and behind the acetabulum; also from the upper half of the hinder surface of the femur, on one side being prolonged up to the tibial, or outer, and on the other up to the fibular, or inner, trochanter. The two portions-the iliac and the femoral portion-are quite distinct, though stated by Meckel not to be so in the Bat. Its tendon descends along the back of the thigh, over the projecting knee, to a ridge-like process on the middle of the posterior and upper edge of the tibia, which is not so large as that in the bird, but rises rather more directly upon the joint. There is no patella. The absence of the patella may be associated with the circumstance that little or no weight is borne upon the hind limbs in these animals and that, consequently, the pressure of the extensor tendon upon the femoial condyles is proportionately small. The view of parts obtained by a dissection of the outer region of the left thigh and haunch, given in PI. VI. figs. 3 and 4 is highly instructive with reference to their comparison with corresponding parts in a fore-limb. The angle formed by the femur with the ilium resembles that of the humerus with the lower or hinder margin of the scapula. The pubes is directed inwards overhanging the joint like the acromion. The ischium is directed backwards and inwards from the joint. The ligamentum teres ascends, from the dimple on the outer and fore-part of the head of the femur, beneath the edge of the cotyloid ligament covering the notch between the pubes and isehium, to the edge of the acetabulum between these two bones, reminding us of the gleno-humeral ligament'. The extensor muscle (Ext. cr.) passes from behind the acetabulum, down the back of the thigh, over the projecting back of the knee, to the hinder edge of the tibia. Theflexors, semni-tendinosus and semi-membranosus, pass from the ischium in front and on the inner side of the joint, over the fiont of the thigh, on the tibial side of the flexors of the foot, to the middle of the fore-part of the tibia. The gracilis passes from the outer and anterior projecting edge of the pubes-like part of the delto-pectoral group in the fore-limb from the clavicle and sternum-and joins the semitendinosus, just as the part of the deltoid in Orycteropus (Vol. ii. p. 299) joins the biceps and becomes a flexor or (which is more appropriate for comparison) as the clavicular or the upper sternal part of the pectoral not unfrequently extends to the forearm or the elbow. The pectineits, adductor brevis, and adductor magnus pass from the crest of the pubes to the outer surface of the femur, just as several parts of the deltoid pass from the acronion and clavicle to the 1 See my Treatise on the Human Skeleton, p. 411. 312 THE MYOLOGY OF THE LIMBS OF PTEROPUS. outer surface of the humerus. The obturator externus passes from the obturator ligament, between the pubes and ischium, over the front of the hip, to the capsular ligament covering the interval between the trochanters and to the inner or fibular trochanter, reminding us forcibly of the 8upraspinatt which passes from between the acromion and the coracoid, over the front of the shoulder, to the capsule between the tubercles. The difference is that this muscle inclines to the outer or radial tubercle and extends beyond the interval between the acromion and coracoid to the dorsum of the scapula; whereas the obturator inclines to the fibular trochanter and is limited by the obtuiator ligament. The psoas magnus and iliacus interns, passing from the anterior and outer surface of the ilium, beneath the pectineus and gracilis, to the outer trochanter, remind us of the infraspinatus and teres minor passing from the outer surface of the scapula beneath the deltoid, to the outer tubercle of the humerus. The glutceus passing from the spines of the sacrum, on the inner side of the extensor muscle, to the inner side of the femur beneath the inner trochanter, is the reminder of the lati'S&'Mu8 dorsi, which takes a nearly similar direction and has a similar attachment in the fore-limb. Gastrocnemius, a delicate muscle, arises from the condyles of the femur in the usual manner, except that it is attached only to the fibular side of the outer or tibial condyle. The inner head (from the fibular condyle) is tendinous; the outer head (from the tibia] condyle) is muscular. There is a minute ossicle in the outer head; I cannot find one in the inner head. Both these heads lie on the inner, or fibular, side of the fiexores curis. They unite and terminate in a thin tendon, which runs down to be inserted into the os calcis. A little above its insertion the base of the styliform bone (St. b.) is closely connected with it. The bone takes its curved course inwards towards the opposite limb in the connecting cutaneous fold, having no direct bony connection. A slip of muscular fibres (S. m. styliform muscle) passes from the proximal end of the fifth metacarpal and radiates out to be inserted along the lower margin of this bone. I do not find any representative of the Solceus or of the Popliteus. The absence of the latter accords with the want of pronatory and supinatory movement mentioned above (Meckel notes the absence of this muscle in the bat). Neither do I find any Plantaris. Tibialis posticus (Tib. p.), small, from the lower half of the nner (fibular) surface of the back of the tibia and from the 313 PROFESSOR HUMPHRY. adjacent surface of the fibula to the tarsal bone supporting the second metatarsal. Meckel thinks it is absent in the bat. Flexores digitorum long, two long and large muscles from the two sides of the leg and the leg bones, separated above by the flexores cruris. One, Tibiatlis (Fl. d. tib.), arises by a large muscular belly from the outer or tibial condyle of the femur, external to and encroaching upon the space usually occupied by the gastrocnemius, from the posterior and outer surface of the tibia, and by a muscular slip from the tendon of the semitendinosus. A muscular slip also is derived from the back of the tibia above the flexor tendons in the position usually occupied by the popliteus. This extends to the inner (fibular) articular surface of the tibia, but does not pass over the joint to the condyle of the femur. The other, fibularis (Fl. d. fib.), corresponding with the FL. 1. h. of man, arises tendinous from the tubercular projection on the fibular side of the head of the tibia, and muscular from the tibia beneath it and from the upper half of the fibula'. Their strong tendons pass through distinct sheaths in front of the ankle; the tibial flexor sends a tendon to the ungual phalanx of the hallux; the fibular flexor sends one to the ungual phalanx of digit v; and the tendons of the two muscles combine to send tendons to the ungual phalanges of the three middle digits. The tibial lies, in the sole, superficial to the fibular; but their three middle tendons are intimately blended. By this blending of the tendons from the two flexor muscles and the non-division of the extensor tendon till it has neared the phalanges, synchronism in the movements of the digits is insured, any one not being moveable alone. The greater individuality in the movement of the digits, especially in the hand, which is so marked in ruan, is in him provided for by the greater separation of the flexor and extensor tendons passing to the fingers and toes. The origin of the tibial flexor of the toes from the condyle of the femur' and from the flexor tendon of the leg is interesting. It has the effect of associating flexion of the toes with that of the leg', and 1 The fibula, though deficient above, is pretty well developed in the lower part of the leg, and has a broad surface at the lower end which is jointed with the os calcis. 2 It is worthy of remark that in birds the flexors of the toes derive origins from the condyles of the femur. 3 Just as, in the bird, the insertion of part of the tensor plicae alaris, from the clavicle, into the supinator longus, which is inserted into the metacarpal of 314 THE MYOLOGY OF THE LIMBS OF PTEROPUS. it has the further effect of causing the forced extension of the leg when the animal is hanging by its curved pedal claws, to give tension to the flexor muscle of the toes. and so increases the grasp of the claws. In short the weight of the animal is thus made to conduce to the firmness of the hold by which the weight is maintained. This connection of the flexors of the digits with the femur is very rarely met with in mammals. Lumbricales are eight in all, and large. One from the tibial or superficial flexor tendon going to digit i. is inserted into the fibular side of that digit; one from the tendon of the fibular or deep flexor going to digit v. is inserted into the tibial side of that digit; the others, arising apparently from the combined tendons of the tibial and the fibular flexors, are inserted one on the tibial and one on the fibular side of each of the other digits. They are inserted, not into the extensor tendons, but into the sides of the shafts of the first phalanges about the middle. The imperfect complement of lumbricales in digits I. and v. shown by the absence of the marginal or distal ones, whereas two are present in each of the other digits, may be regarded as among the many evidences, of which small size is the most obvious, of the incompleteness of these lateral and least constant, last segmented and, as it were, least cared for elements of the terminal part of the limb. The less complete blending of the tibial and fibular components of the flexor muscle in the tendons passing to these digits as compared with those passing to the other digits, as well as the absence of the flexor brevis on the fibular side of digit v. and its total absence in digit I, and the absence of a long extensor in digit i, are features of similar import. Accessories I do not find. Flexor brevis digitorum arises from the os calcis and the lower part of the tendo Achillis on its tibial side-that is, in the situation usually occupied by the plantaris tendon whikh, as I have said, is absent. It passes to the second phalanges of digits ii, III, and iv, splitting to permit the long flexors to pass just as the corresponding tendons do in man, and reuniting above them. It passes also to digit v, but only to its fibular side. Interossei constitute a pair of muscles on the plantar surface of each of the metatarsals, arising also from the tarsals, ten in all. One is on the tibial and one on the fibular side of each the pollex, serves to associate extension of the carpus and digits with that of the forearm. 315 PROFESSOR HUMPHRY.. metatarsal. They pass to the tibial and fibular sides of the palmar surface of the first phalanges of their respective digits a little beyond their proximal ends. I could not trace them to the extensor tendons. They act chiefly as flexors of the first joints of the digits'. Abductor minimi digiti, a short, thick muscle extending from the os calcis, near the insertion of the tendo Achillis, to the fibular side of the fifth metatarsal. Transversus pedis (Tr.) is a distinct muscle arising from the inner cuneiform bone, from the fibular side of the proximal end of the first phalanx of the hallux, and from a tendinous arch between these two points, beneath which passes the fibular interosseous of the hallux. From this broad origin the fibres converge to the tibial side of the first phalanx of the fifth digit, where they are blended with the interosseous of that side. It corresponds, apparently, with the 'adducteur transverse' of Cuvier, who does not mention its presence in this animal. The metatarsals admit of a certain amount of lateral movement, abduction and addiction, which is effected by the alternate action of this transversus and the tibialis anticus and the peroneus brevis aidpd somewhat by the lateral interossei. The peroneus longus not passing to the metatarsal of hallux and playing little or no part in abduction may be a reason for the presence of this transversus. Moreover the interossei are more parallel than usual, and those to the lateral digits (i. and iv.) do not extend across so as to serve as adductors, which is an additional reason for the presence of a distinct and well developed transverse muscle. It will be observed that the separators of the metatarsals-tibialis anticus and peroneus brevis -are on the dorsal or extensor aspect of the limb, and the approximator of them-the transversus-is on the plantar or flexor aspect. With regard to this association of abduction with extension and of adduction with flexion, see preceding Vol. p. 306. Tibialis anticus (Tib. a.) descends as usual from the fibular surface of the tibia, over the tibial side of the tarsus, and is inserted into the tibial side of the first metatarsal, abducting it and turning the foot outwards. Extensor digitorum (Ext. dig.), from the fore part and the fibular side of the head of the tibia. Its long tendon passes over the tarsus and metatarsus and, near the phalanges, radiates into four slips to the four small toes. It is a delicate muscle; 1 See remarks on the arrangement of the interossei in preceding Vol. p. 305. 316 THE MYOLOGY OF THE LIMBS OF PTEROPUS. Extensor brevis, comparatively strong, arises from the front of the os calcis and the back of the metatarsals. It passes as usual to the four, in this instance, outer digits (i, II, III, Iv.), being the only extensor of the hallux. Its four divisions are distinct, each lying along its metatarsal bone. The two middle, to digits ii. and iii, present a longitudinal separation, somewhat reminding us of the interossei on the plantar aspect. These divisions join the long extensor tendons, one portion of each joining the fibular and the other the tibial edge of a tendon. The division to digit iv. is developed, or well developed, only along the fibular side of the metacarpal, and joins only the fibular side of the extensor longus tendon, which is the usual disposition of the extensor brevis in the case of all the digits in other animals. The division to digit I. is large, is inserted partly into the back of the first phalanx, and sends a delicate tendon along the back of this phalanx to the base of the second phalanx. The distribution of the extensor brevis to the two sides of the extensor tendons of digits ii. and ini. is interesting in connection with the anatomy of the lumbricales. Usually the tendons of the extensor brevis lie only on the fibular sides of those of the extensor longs; and to balance them, as it were, the lumbricales pass to the tibial sides of the tendons of the extensor longus. But in this instance there is a greater completeness and separation of the extensor brevis and the lumbricales: the tendons of the former pass to both sides of the tendons of the extensor longus and the lumbricales have no connection with the extensor tendons, pass on both sides of the phalanges, and are inserted into them. Peroneus longus, from the fibular side of the head of the tibia and the septum between the extensor and the flexor digitorum descends, in front of the lower end of the fibula, through a groove on the outer side of the tarsus, to the under part of the proximal end of the second metatarsal bone. I cannot trace it to the metatarsal of hallux. Peroneus tertius, rather large, from front of fibula, beneath and internal to extensor digitorum, to metatarsal bone of digit v. In the male it sends a tendon to join the extensor tendon of this digit; and there is also a small slip to this digit from the extensor brevis. In the female this slip is wanting; but the peroneal tendons to the extensor and to the metatarsal are from 317 PROFESSOR HUMPHRY. distinct muscles. Thus the extensor tendon of digit v. is supplied from two or three sources, whereas that to hallux is derived only from the Ext. br. No other peroneus present. Meckel finds only one peroneus in Cheiroptera. PLATE VI. Fig. 1. Muscles on the abdominal aspect of male Pteropus. The right hind-limb has been partially and the left has been much turned or rotated from the natural position for the purpose of showing the muscles on the two surfaces. 1. 2. 3. 4. The facial, occipital, cervical and sternal portions of platysma uniting to form 5 the tensor plicse alaris, which is elastic from near the convergence of the muscular bundles to a, between a and b is again muscular, and between b and its insertion is tendinous. St. h., sterno-hyoid. Digr., Iigastric. Tr. in., trachelo-mastoid. St. ct. m., sterno-cleido-mastoid, from the anterior extremity of the keel, from the upper edge of the keel (this is rather in shade) and from the clavicle. Subcl., subclavius. C. A., cervico-humeral. R. a., rectus-al)dominis. The sternal portion of the first rib is seen between this and the subelavius. RIGHT FORE-LIMB. Pect., sternal portion of pectoralis major divided and reflected from its origin. Pect. a., abdominal portion of pectoral. The clavicular portion has been removed to show subclavius. B., biceps. C. b., coraco-brachialis. Br. a., brachialis anticus. Ext. c. r., extensor carpi radialis. Sup. 1., supinator longus. Pr. t., pronator teres. El. c. r., flexor carpi radialis. Fl. d. s., flexor digitorum sublimis. Fl. c. u., flexor carpi ulnaris. RIGHT HIND-LIMNIB. Ps. p., psoas parvus. Ps., psoas magnus It. i., iliacus internus. P., pectineus. Gr., gracilis. F. c., femoro cutaneous. Fl. d., flexor dig. long. P. I., peroneus longus. Ext. d., extensor digitorum. P. 3, peroneus tertius. fib. a., tibialis anticus. LEFT HIND-LIMB. Gr., gracilis. Ad., adductor muscles. S. in., semi-membranosus. S. t., semi-tendinosus. I. c., ischio-cutaneous. St. m., styliform muscle. St. b., styliform bone. 1. Ach., tendo Achillis. Fl. d.fib., flexor digitorum fibularis. Tib. p., tibialis posticus. Fl. d. tib., flexor digitorum tibialis. LEFT FORE-LIMB. Fl. br., flexor brevis, ' interosseal flexors' of digit v. Abd., abductor of digit v. Fl. c. r., flexor carpi radialis. Fl. d. pr., flexor digitorum profundus. Fl. d. s., flexor digitorum sublimis. Fl. c. u., flexor carpi ulnaris. Pr. t., pronator teres. Sup. I., supinator longus. Fig. 2. The right side of pelvis femur and upper part of tibia, of male Pteropus. It., upper part or crest of ilium. C., crest of pubes where psoas parvus and pectineus are attached. S., symphysis pubis. ech., ischium. 318