110 PEOCEEDINGS OF THE NATIONAL MUSEUM vor.. 7.:i 



the ear laps at the base, so that when the ear is pulled backward by 

 the cervico-auricular musculature, flexion of the mandibulo-auricu- 

 lar complex furls the base of the pinna and effects complete closure 

 of the tube. There is no conspicuous valve within the tube. In 

 Plioca his'pida conditions are considerably different, for there is no 

 external ear or pinna. Near the orifice, however, there is a small 

 fibrous pluj,^ which acts as a valve to close the tube upon contraction 

 of the mandibulo-auricular. No action of the cervico-auricular mus- 

 cles could be detected in living animals. Dissections of Ernst 

 Huber, however, indicate that there is considerable specific variation 

 in the mechanism for dosing the ear of the Phocidae. 



The auditory tube is not longer in the phocid, and so the external 

 auditory orifice is really no farther dorsad in this animal than in 

 the otariid, but the sagittal line is higher in the latter, and this 

 increases with age, so that in reality the top of the head is higher 

 above the ear and the head must be thrust higher out of water for 

 the animal to hear. In the phocid the eyes also are directed more 

 dorsad (15° to the vertical as against 50° in the otariid), and the 

 external nares as well (45° to the cranial axis as against about 20° 

 in Zaiophus), so that eyes, ears, and nostrils are so placed in the 

 earless seal that these organs of sense may be utilized while the 

 animal exposes the minimum amount of its head above the surface 

 of the water — a definite aquatic modification developed to a greater 

 degree than is the case in Zalophus. 



Quite diverse stimuli seem to have been instrumental in molding 

 llie characteristics of the neck in the otariid and the phocid. In 

 adult bulls of the former the neck acts partially as a repositoiy for 

 surplus fat accumulated to sustain the animal during the breeding 

 season. Unfortunately proof is at present impossible, but I am 

 strongly of the opinion that at the approach of the breeding season 

 when the otariid bulls must do battle for the females, the increase in 

 the swelling of the neck is also partially due to an enlargement and 

 coarsening of certain of the cervical muscles, this action being caused 

 by a hormone or similar secretion of the awakening sex glands. 

 This had puzzled me for some time until O. J. Murie informed me 

 that he had noted a great increase in size of certain neck muscles 

 (chiefly the sternomastoid I believe) during the rutting season of the 

 caribou {Rangifer) ^ the purpose of which is evidently to add to the 

 fighting ability of the bulls. This is entirely comparable to the 

 relatively great increase in the length and size of some of the perineal 

 muscles of female mammals at the imminent approach of parturition. 



This cervical swelling does not take place in females and young 

 bulls of the Otariidae. Even in old bulls submersion lightens the 

 weight of the neck, and the more powerful musculature of this sex 

 may theoretically handle the large neck even more agilely under 



