446 DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 
tendons. The arrangement of these latter, therefore, is in accordance with what 
obtains in Ursus americanus as depicted in the ‘ Recueil’ of Cuvier and Laurillard. 
Whether entire suppression of the extensor indicis proprius has taken place in the two 
last mentioned Pinnipeds, or the so-called extensor medii digiti is but a differently 
inserted condition of its tendon, I will not pretend to say. 
The extensor minimi digiti (£.m.d), like the last, is single as far as the wrist, where 
its tendon splits into two, which lie alongside each other, but on opposite sides of the 
fifth metacarpal. 
That which gives such great power to certain movements of the manus in Ofaria (to 
wit, the extraordinarily developed tendon of the extensor pollicis et indicis, Wood)! is 
much less remarkable as regards strength and breadth in T'richechus (woodcut, fig. 3, 
Ep Gi). In the latter animal it is also observed to divide, or rather present dense 
tendinous fasciz running to the outer side of the distal end of the pollicial or first 
metacarpal bone. Whilst the Seals have nearly the same disposition of pollicial 
muscle, it is slenderer as to tendon and belly than either of the above. Although the 
pollex alone receives a tendon in the Pinnigrades, and ‘long extenseur du pouce” of 
Duvernoy may be a correct term, yet Wood’s name, here used, is expressive, inasmuch 
as it points to the division of tendon evidently of the similar muscle met with in the 
Black Bear, Coati, Lion, &c., and to its still greater differentiation or doubling of belly 
in the Panther and other forms. 
The fore limb of Trichechus diverges from that of Otaria and Phoca in possessing 
representatives of the extensor ossis metacarpi pollicis, extensor primi internodii 
pollicis, and extensor secundi internodii pollicis, the last forms having only one 
distinct muscular belly and a single tendon. In the first-mentioned animal a cursory 
examination leads to the supposition that the extensor ossis metacarpi pollicis alone is 
present ; but dissection proves the contrary. The muscles in question are best traced 
from the tendons upwards. ‘The three together are inserted in an aponeurotic sheath 
at the root or proximal end of the pollicial metacarpal. One slightly overlaps the 
other, the extensor ossis metacarpi pollicis being superficial and outermost. The 
middle tendon, or that of the extensor primi internodii pollicis, is the smallest; whilst 
the deepest and innermost tendon is that equivalent to the extensor secundi internodii 
pollicis. (See woodcut, fig. 3, E.p.i.p. £c.) 
Over the dorsal surface of the lower portion of the radial shaft their muscular bellies 
commence, and with considerable union may be traced upwards, becoming broader and, 
indeed, as a whole, triangular. 
The extensor ossis metacarpi pollicis is attached chiefly to the back of the radius and 
interosseal membrane, though it is also fixed to the outer condyle; its innermost 
portion is the longest. 
The small tendon of the extensor primi internodii pollicis, on altering upwards to a 
* Loc. cit. 1867, yol. xv. p. 533. 
