ABT. 15 ANATOMY OF THE EARED AND EARLESS SEALS HOWELL 111 



water than is the case with females and young males. At any rate, 

 even though the neck is relatively no longer than in the cat, it always 

 has the appearance of being long and flexible, capable of great con- 

 tortion and great precision of movement. This has been developed 

 in the pursuit of agile prey, necessitating darting movements of the 

 head here and there, and also in the sinuous movements which this 

 family is seen to use while swimming, thrusting the head this way 

 and that as an accessory rudder in aid of the more posterior one (the 

 hind feet), with the middle thorax as the fulcrum of leverage. For 

 the reason that natation is almost exclusively by means of the fore 

 feet, this sinuous development of the neck has not been inhibited by a 

 more powerful stimulus, as seen to best advantage in Cetacea and 

 to a lesser extent in the Phocidae, in both of which the neck acts as 

 part of the fulcrum upon which acts the lever of the posterior end 

 of the animal during swimming. The mobility of the head and neck 

 of the otariid is further increased by the part which they play in 

 terrestrial locomotion, during which the neck violently sways back 

 and forth, not only to maintain proper balance, but as a direct aid, 

 chiefly through the broadened cepahlohumeral, to rhythmic motions 

 of the forelimbs. Besides the cephalohumeral, other broad muscles 

 which aid in diverse movements of the head are the anterior rhom- 

 boid, splenius continuous with the trachelomastoid, and the broad- 

 ened insertion of the sternomastoid ; and the exceedingly complex 

 third or atlantic division of the longus colli must also have an 

 important bearing in this connection. 



There is apparently no reason why an agile neck would not be of 

 great advantage to a PJioca also, and it is not meant to imply that 

 this member is actually stiff. But the fact remains that extensive 

 observation of both sea lions and seals shows that the latter uses its 

 neck in a different manner. It seems actually to have extensibility 

 and may be stretched to a surprising degree, but in retrieving a dead 

 fish there is not the speedy action and " catch on the fly " of the 

 otariid, but a more deliberate nuzzling and capture, nor is the head 

 and neck moved much as an aid to terrestrial progression. The 

 articulations of the vertebrae are doubtless as free, but the muscles 

 are apparently used in a different manner. Largely instrumental 

 in this lack of agility is the fact that in this family, as in the Cetacea, 

 practically all the motive impetus during aquatic progression is fur- 

 nished by the extreme posterior end of the animal, and the neck as 

 well as the anterior thorax acts as the fulcrum upon which works the 

 powerful musculature of the lower back. The head, together with 

 the forefeet, doubtless plays a most important part as a rudder, but 

 in very circumscribed movements, for a slight twist dorsad or laterad 

 would be all that was necessary. In other words, no animal tliat 



