DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 447 
muscular belly, runs into that of the extensor ossis metacarpi pollicis, and cannot well 
be divided from it. The extensor secundi internodii pollicis goes chiefly to the entire 
shaft of the radius and interrosseous membrane and olecranon process. 
Having in Ofaria fully described the broad and multiple long superficial palmar 
muscles, and the unusual strong sheet of tendon forming the palmar fascia and oblique 
ligamentous band acting upon the pollex, I need here only add that Trichechus has 
nearly a similar distribution of muscular and tendinous structures. In our young spe- 
cimen of the latter the following differences were noted :—The tendon inserted on the 
deep surface of the palmar fascia of the palmaris longus primus was not so distinct. 
The special broad aponeurotic slip (palmaris longus secundus) to the distal end of the 
fifth metacarpal was not nearly so strong and ligamentous. Lastly, the fleshy belly of 
the palmaris longus tertius was relatively much weaker, but also fused with the flexor 
carpi ulnaris; and the oblique palmar tendon and aponeurosis was decidedly thinner 
than in the Eared Seal. 
Another very characteristic differentiating feature in the manus of the Morse from 
that of the Sea-lion is the development of a flexor brevis manus (woodcut 4, F.b.m). 
This muscle is composed, at its origin on the deep surface of the palmar fascia, of a 
single narrow fleshy band, which at the proximal ends of the middle metacarpals divides 
into three small fusiform bellies, which end in delicate tendons. Each of these tendons, 
at the distal ends of the second, third, and fourth metacarpals, joins the perforated 
tendon and is lost therein. It was noticed particularly of that to the second that it 
split and allowed the perforans to pass through. Such may have been the case with 
the other two; but this was not observed. 
Neither the fleshy origin nor insertion of the flexor carpi ulnaris (woodcut 4, F.c.w) 
is with certainty divisible from the so-called third or ulnar palmaris longus, the only 
distinguishable portion being the broad tendon fixed to the pisiform bone; but even this 
has aponeurotic connexion with the oblique palmar fascia. 
In O. jubata there is no pronator quadratus; but in the Walrus it is undoubtedly met 
with and fairly developed (woodcut 5, P.g). It exists as a thin fan-shaped sheet of 
muscular substance with a superficial intermixture of tendon. The ulnar attachment, 
nearly 13 inch broad, is quite at the distal end of that bone, and partly on the inter- 
osseous ligament. Set obliquely upwards and outwards, it is inserted into the shaft of 
the radius above its lower expansion, where it is less than an inch broad. 
The muscles representing the sublimis, profundus, and flexor longus pollicis in the 
Morse have a partially different tendinous distribution from those of the Sea-lion. 
What may either represent the flexor sublimis digitorum, or, conjoined with it, the 
flexor profundus digitorum, is a double-bellied muscle. One head, as in Otaria, arises 
from the internal condyle and capsular ligament, the other from the inner surface of 
the ulna below the olecranon ; and these two elongated flattish bellies run separate to 
the wrist-joint, each being tendinous, however, an inch above that. 
