DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 445 
There is such union between the extensor carpi radialis longior and extensor carpi 
radialis brevior (woodcut, fig. 3) that what appears but a single muscle represents them 
both. At the proximal ends of the pollicial and indicial metacarpals an aponeurotic 
or strong firm tendinous expansion terminates the single tendon of the muscular belly ; 
and this is attached equally to both the above bones. 
I have remarked, in the myology of Otaria jubata, that there are a double set of 
extensor muscles of the antibrachium arising from the outer condyle. This is the case 
in Trichechus rosmarus; but that portion of the group to which I have applied the 
designation of extensor communis digitorum in the former animal, has in the latter the 
tendons inserted into the proximal ends of the first phalanx, though continued further 
in a sheath of fascia. The great fibrous interlacement notable in the Sea-lion is not 
so strong and distinct in the Walrus; the latter consequently has greater flexibility at 
the wrist. After all, this pliability of the manus may be as much dependent on the 
young condition of the specimen as on the junction or segregation of the tendons, the 
less-ossified state of the bones and rigidity of the interarticular cartilages being in 
favour of such a view. 
What represents the extensor communis digitorum (woodcut, fig. 3, H.c.d) has a flat, 
broad, thin belly, which at the distal end of the radial shaft splits into three tendons 
destined for the second, third, and fourth digits, these being inserted respectively into 
the distal end of the first phalanx. That to the fourth splits at the wrist; but the 
separate tendon again joins its fellow at the middle of the first phalanx. The said 
tendons in the Walrus are altogether smaller than in the Eared Seal. In Phoca the 
the common extensor splits into four digital tendons—an arrangement agreeing with 
that in most Carnivores. 
The second belly, coequivalent with the extensor medii digiti of Wood’ (E.me.d), is 
likewise a thin, broad, and flat muscle. It is very closely adherent to the above; but 
intermuscular fascia separates them, and about the middle of the radius this uncommon 
strong fascia, gaining strength and the appearance of a tendon, is fixed into the ulnar 
margin of the bottom of the shaft of that bone. The fleshy portion of the extensor 
medii digiti leaves that of the extensor minimi digiti near the wrist-joint, where it 
passes through a separate cross loop of binding fascia, and sends onwards a single 
tendon to the interspace between the fourth and fifth digits, where it splits into four or 
five short tendons. 
In the common Seal, as Duvernoy’ has noted, the index receives a tendon as well as 
the median digit ; and to the muscle in question he applies the term “ extenseur propre 
de Yindex.” In the Otary and Morse, however, there is no special indicator*, the said 
medii digiti in the former supplying the third and fifth digits with well-developed 
* Myological papers, Proc. Roy. Soc. 1866 et seq. * Mém. du Muséum, t. ix. p. 68. 
* What Sir Everard Home (Philos. Trans. 1824, p. 239) denotes as an “indicator muscle,” I presume is the 
“long extenseur du pouce” of Duyernoy, and what I allude to as the “ extensor pollicis et indicis ” of Wood. 
3Q2 
