DR. J. MURIE ON THE ANATOMY OF THE SEA-LION, 567 
the ordinary double interosseous muscles to each metacarpal bone, there are two extra 
superficial ones, which, along with the abductor minimi digiti, may be said to form an 
upper series of short metacarpal flexors. 
Superficial Layer of Interossei. What I shall describe as the first of these is a 
moderate-sized fusiform muscle (fig. 28, S.'). This arises by tendinous fascia, as 
much as by a defined tendon, from the broad carpo-metacarpal palmar ligament to the 
ulnar side of the third digit; passing forwards and towards the radial side of the third 
metatarsal bone, it is inserted by tendon. The second superficial interosseous muscle is 
of about equal size with the last. It also (S.J) is fusiform, and arises by tendon from 
the same deep palmar fascia or ligament. It, however, crosses the tendon of the first- 
mentioned muscle ; and its direction is the reverse, viz. from the radial towards the ulnar 
side, being inserted by tendon to the radial side of the fourth. 
Deep Layer, or Interossei proper. Ist. The pollex has a single, large and powerful 
interosseus muscle (1), which lies to the outer (radial) side of the metacarpal bone. It 
has origin, along with the outermost indicial interossei, from the deep fascia and palmar 
carpo-metacarpal ligament, and is inserted by a longish strong tendon into the sesamoid 
cartilage on the radial side of the pollex, at the proximal end of the first phalanx. 
2nd. The index has a pair of interosseous muscles (2) of smaller size than the pollicial 
one. The ulnar one of these two arises along with that described as going to the 
pollex, and is inserted into the ulnar side of the second digit. The radial one arises, 
partly tendinous and partly fleshy, from the deep palmar carpo-metacarpal ligament to 
the radial side of the second digit. It is inserted, by a short but strong tendon, into 
the radial side of the same digit. 3rd. The third digit is in like manner supplied by a 
double interosseus muscle (3), one belly to the radial and the other to the ulnar side. 
4th. The fourth digit is also provided with a pair of these muscles (4), which, while 
palmar, are divisible into a radial and ulnar one. They, however, while still fleshy, are 
shorter than those already described; in this respect they agree with the retrogressive 
shortening of the metacarpal bones from the first to the fifth digit. 65th. The pair of 
interossei of the fifth digit (5) are more closely united than the others. They are 
altogether smaller, and lie more upon the middle and plantar surface of the metacarpal 
bone. ‘They are both inserted upon the outer side. 
7. Muscles of the Posterior Extremity. (Plates LXX. & LXXTIL.) 
In none of the larger Mammalia, not even in the Earless Seals, are the muscles con- 
stituting the buttocks so altered in their relations and general appearance, and yet 
withal so well developed as in the Otaria and Trichechus. This arises mainly from the 
curious position which the femur has assumed, and by that banding together, as it were, 
of the lower legs—the natural position of the hinder extremities, when the animal is 
walking, reminding one of the position of the frog’s legs when flexed preparatory to 
the act of striking outwards and backwards in swimming. 
VOL. VII.—PART VI. January, 1872. 4M 
