THE NECK 



Taylor (1914) stated that the neck of the sea otter is two-tenths of 

 the trunk length, while it is three-tenths in the river otter. With this 

 exception it seems that all aquatic mammals other than the Cetacea, 

 Sirenia and Pinnipedia are either insufficiently specialized to exhibit 

 alteration in the length of the neck, or else they have no terrestrial rela- 

 tives close enough for significant comparison. 



It is from the Pinnipedia and Cetacea that we can tell most about the 

 effect which speedy aquatic locomotion has had upon the neck, and they 

 will be discussed at considerable length. They are amenable to two 

 sets of fundamentally different influences imposed by widely diverse 

 swimming methods. The Phocidae or true seals together with the Ceta- 

 cea comprise one group, and in this really belong the Sirenia as well. 

 The other group consists of the Otariidae of fur seals and sea-lions. The 

 walrus {Odobenus) occupies an intermediate position in some respects. 

 The differences in these two methods of swimming which are of concern 

 to us in the present instance is that in the first group the locomotive im- 

 pulse is purely from the rear, while in the second it is from the anterior 

 thoracic region. 



The cervical complex of the Otariidae is long and sinuous, and the 

 function which it, with the head, plays is two-fold. The animal when on 

 land travels by a shuffling gallop, a gait made necessary by the shortness 

 of its limbs. This is accomplished only by the expenditure of much 

 effort and is greatly facilitated by the violent swinging backward and for- 

 ward of the neck. Especially is this so in the case of large bulls with 

 huge mass of cervical tissue. This swinging of the neck is an absolute 

 requisite for their terrestrial mode of locomotion. If the neck were but 

 half its length it is likely that travel upon the land would be so difficult 

 that they could do little but wriggle onto a rocky ledge and roll off 

 again. 



In swimming, the impulses are from the side in the case of Otariidae, 

 with the center of motion presumably between the two organs for pro- 

 pulsion and near the midthorax. Conditions are thus very similar to 

 the case of a rowboat. A short, tubby skiff is difficult to handle, and 

 one of usual length is best managed when the rower is near the center. 

 Thus, for mechanical reasons, the sea-lion should have considerable 

 mass of body both before and behind the anterior flippers, and this has 

 undoubtedly constituted the chief stimulus for length of neck in this 

 animal. Whether this has been of any influence in the acquisition by 

 adult bulls of their enormous mass of cervical tissue seems doubtful, 

 but must be considered as a possibility, in which case there would have 



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