DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 423 
On comparison with measurements taken to the same points in Ofaria, I find that 
the young Trichechus is relatively and absolutely shorter-limbed. The brachial girth 
close to the body is almost identical. The greatest diameter or breadth presents agree- 
ment; but Ofaria has rather the advantage. The Morse has the thickest manus. The 
anterior curved and free margin has a length greatly in favour of the Sea-lion; but in 
the posterior concave or axillary border the reverse obtains. Thus it results that the 
available area for impulsion in water is less in the Walrus than in the Eared Seals; and 
this is in accordance with what is known of their swimming-power, which is far inferior 
to that of the Otaries. 
7. Ventral Region.—Strictly speaking, the Walrus possesses no free tail, as do the 
Phocide and Otariide; for a broad web of skin stretches across from os calcis to os 
calcis, enveloping the caudal representative. This remarkable elastic membrano-tegu- 
mentary expansion, reminding one of the more delicate web similarly situated in Bats, 
has posteriorly, when the legs are outspread, a wide semilunar border with little if any 
medio-caudal projection. What appears as a tail when the limbs are approximated 
(Pl. LIV. fig. 12, ¢), is in reality fibroid tissue and skin; for the caudal vertebre stop 
short about an inch from the free margin. 
The opening of the anus is within 13 inch of the tip of the tail, the latter, as has 
been said, being outwardly well nigh obsolete, so much covered is it by the caudo-leg 
membrane. Even when examined belly upwards the anal aperture is not freely exposed, 
being covered or overlapped by a kind of duplicature of the said loose expanse of skin 
(af ), which, indeed, forms part of the ordinary rectal folds often met with in this region. 
There is an indistinct linear raphe present, most marked close to the rectum. The skin 
in the region posterior to the anus and fold has a punctated character, arising from the 
distribution of cutaneous glands (Pl. LIV. fig. 13, 7). Narrow, linear, transverse or 
oblique rugz are also present at this part. The ventral surface of the diminutive tail 
appears raised above the adjoining membrane, and in the present instance was cicatrized, 
evidently the healed scar of a former wound. 
The external orifice through which the penis protrudes in erection shall be described 
along with the organs of generation. Some 5 inches forwards from the anterior border 
of the aperture, the umbilicus (fig. 14, wm, Pl. LIV.) is met with. This is a deepish 
pit, with an elevated roundish projection of bare skin as large as a shilling in circum- 
ference, and, besides minute circular rug, is marked by a dozen or thereabouts of deep 
radiating furrows and ridges. 
Professor Owen notes (J. c. p. 104), as does Daubenton in the foetus (op. cit. p. 420), 
that there are four mamme in the female—two abdominal, and two inguinal. I observed 
the same number of teats in this young male; they were buried, however, in depres- 
sions, and not elevated as in the adult male Ofaria. The two posterior teats were 
situated opposite the anterior border of the opening for the penis, but at 53 inches 
outward distance from it. The anterior pair were 9 inches in advance of them. 
