ECOLOGY AND BIOLOGY OF THE PACIFIC WALRUS 



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Fig. 43. Innervation of the mystacial vibrissae and snout in a 4-year-old Pacific walrus. 

 Skin and part of musculature removed from the right side of the face, exposing the eye 

 (E), jaw (J), external nares (N), and the bone surrounding the root (R) of the tusk (K). 

 Large branches from the facial (F) and trigeminal (T) nerves enter the proximal end of 

 each vibrissa (V); other branches enter the intervening rostral musculature (M). (Photo 

 by F. H. Fay) 



400 to nearly 700 per walrus and are situated in 13 to 18 rows on the anterior 

 surface of the rostral pad. I counted them in one adult female and found 468. 

 According to Kosygin (1975fo), the mean number per side is slightly greater in 

 males (242.48 ± 4.65) than in females (223.68 ± 3.05). 



The mystacial vibrissae of the walrus have a smooth surface and are oval in 

 cross section; the ratio of least: greatest diameter is about 3:4. In the adult, these 

 hairs are whitish to yellowish and translucent, with an opaque medulla in which 

 there are no air spaces. The root of each is enclosed in a stout capsule of 

 connective tissue, to which many fine strands of striated muscle are attached. 

 Within the capsule, the hair is surrounded by a series of sinuses, typical of 

 sensory hairs. The upper and lower blood sinuses are relatively smaller and the 

 ring sinus and Ringwulst relatively larger than those in the elephant seal 

 (Mirounga) described by Ling (1966). 



The principal nerves serving the vibrissae and the muscular rostral pad are the 

 maxillary branch of cranial nerve V (trigeminal) and the dorsal buccal branch of 

 cranial nerve VII (facial). Both of these are unusually large in the walrus, and 

 their fibers combine partially in the vicinity of the tusk socket (Fig. 43). From 

 that point, they radiate into the rostral pad, sending a large branch to the 

 proximal end of each vibrissa follicle and others to the intervening muscles and 

 skin. 



