460 DR. J. MURIE ON THE ANATOMY OF THE WALRUS. 
manus, which, however, is met with in Phoca. The splitting or subdivision of the 
extensor ossis metacarpi pollicis marks variation from the Eared and Earless Seals. 
In the superficial and deep long palmar muscles and tendons some differentiation is 
witnessed, whilst the palmar fascia is not nearly so dense as in the great flipper-like 
manus of 0. jubata. The latter possesses a flexor brevis minimi digiti, which the Morse 
has not. A single lumbricalis has been found equally in the Seal and in the Walrus. 
The extensor brevis digitorum has an increased number of bellies; and instead of an 
accessorius, a short bridging tendon between exists. 
The veins in the Walrus, as in the Seals and Otaries, evince adaptation to frequent 
aquatic submergence—this by their great capacity towards the root of the heart, and by 
the enormous cava or hepatic reservoir. The widened aortic arch and diminution of 
the abdominal aorta modify the current, the vast muscular apparatus of the fore 
quarters and large brain receiving the major share of supply; and the tendency to rete 
mirabile observed in the extremities spreads out the blood’s force so that a slow but 
steady current is ensured. The glands, thoracic, axillary, inguinal, and ischiatic, are 
numerous, large, and surrounded with vascularity; and here I am inclined to think, 
under certain conditions, stasis of the circulation temporarily takes places. After 
repeated conversations with men who have often watched young Seals in a state of 
nature, and my own anatomical observations upon animals of various ages, I am 
satisfied that what Dr. Wallace! and Mr. Brown state bears the stamp of truth, viz. that 
expertness in swimming and power of remaining long under water is an acquired habit. 
There is this, however, to be said, that the vascular distribution and reservoirs inhe- 
rently allow of further development? through use accruing; the Walrus forms no 
exception. It is useful to reflect on the manner in which long submergence is provided 
for in the air-breathing Sirenians and Cetaceans, 7. e. by intercostal plexuses and mani- 
fold retia mirabilia. 
Voice in a great measure is suppressed in Cetacea ; and as the enlarged arytenoids are 
thrust upwards towards the spiracle or nares, breathing ensues. In Sirenia the nostrils 
are situate nearer the muzzle; the larynx in diminution and form resembles more ter- 
restrial mammals; but the lungs, unlike those Whales, are extraordinarily lengthened. 
The Walrus and Seals revert more to land breathers. Still the lungs have great mag- 
nitude; but the laryngeal apparatus is modified by the increment of the arytenoids, 
atrophy of the epiglottis, and full development of the pharyngeal constrictors and 
uvular curtain, so that powerful inspiration and expiration are effected as the surface of 
the water is reached. 
As to the visual organs in the Walrus, they pertain to the Carnivorous type, adapted, 
however, to media of different refraction. 
1 P. Z.8. 1868, p. 408. 
* If an example were needed, the mode in which varicose veins are produced in the human subject might be 
cited. 
