DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 459 
Skin-folds, such as have been described in the Trichechus, are, comparatively speaking, 
absent in Ofaria and Phoca. 
The Pinnipedian act of locomotion, both on land and in the water’, is a study of 
the highest interest, and, from an almost fish-like movement in some, transitionally glides 
in others to the motions pertaining to ordinary terrestrial Mammifers. In the water 
the Seal progresses alone by its hind feet, used almost like a piscine tail; the Sea-lions 
(and Sea-bears?) progress with extraordinary speed by dint of alternate sweeps with 
their enormous pectoral limbs, the pelvic limbs being kept in abeyance or simply 
employed as steering-apparatus. The Walrus in the same element simultaneously 
lashes its posterior extremities curvilinearly or Seal-fashion ; but, besides, it reciprocally 
moves its anterior extremities, somewhat after the manner of Otaria. 
On land, the total suspension of the limbs as motor agents, and instead a saltatory 
wriggling abdominal movement, pertains to the Seal, though I have observed in the 
Phoca grenlandica an intermediate stage in an occasional use of the fore feet; the 
Otary manifests increased power of limb in its hobbling plantigrade walk; and as the 
Morse is reached a still further deviation from the Seal towards the Bear tribe is shown 
in the greater freedom of use of the pelvic limbs. 
Modifications trending in a similar direction are witnessed in the less or greater 
freedom of limb-attachment, in the development of axillary and caudo-tibial tegument, 
lowering of muscular insertions, in ligamentous union, and, lastly, osseous apposition. 
We have only attentively to watch the Ursine walk to become convinced that the 
way in which the fore limbs are thrust forwards and the hind legs bowled along, is but 
a remove from the constrained and more fixed heel-action of the Walrus. Indeed, in 
examining a Polar Bear some few years old, I could not but acknowledge that the 
pelvic extremities, seen from below, only required a slight extension of the ischio-tibial 
parts, and corresponding reduction of the already short tail, to transform them into the 
condition which obtains in the Morse. 
Considering the very different attitudes assumed by the Trichechide and Otariide as 
compared with the Phocide, it is remarkable how very little deviation follows in the 
muscular development. The two former, as might be anticipated, present a general 
agreement, especially in the mode of implantation of the muscles of the hind leg, and 
in this respect recede from the Seal, yet but slightly. The first-mentioned possess 
several muscles not found in the second, The variations of minor importance have 
sufficiently been dwelt on; it is only necessary therefore to advert to the more striking 
points. Amongst such are the presence of a coraco-brachialis, a flexor brevis manus; 
a pronator quadratus, an opponens pollicis, and a paimaris brevis. The large size of 
the auriculares is remarkable when deficiency of a concha is taken into account. There 
is a distinct fleshy external anconeus, as in Otaria, and a double set of extensors of the 
* Consult the researches and masterly analysis of these movements, as bearing on the mechanism of flight, 
by Dr. J. B. Pettigrew, Trans. Linn. Soc. 1867, vol. xxvi. p. 207. 
VOL. VII.—PART VI. June, 1871. 38 
