THE NECK 



the number of cervical vertebrae, which hmits agihty, while the vertebrae 

 of this region in reptiles are as remarkably plastic, and may multiply in 

 some manner or other to a phenomenal number, allowing a length and 

 mobility of neck utterly unattainable in mammals. So an aquatic reptile 

 with a figure suggestive of a wash-tub may have a neck like the half of 

 a huge snake, with as many as 76 cervicals in some plesiosaurs, enabling 

 it to strike at and seize a fish which the body would be incapable of over- 

 taking. 



There are two body forms that an aquatic mammal might assume al- 

 lowing either a lengthening or shortening of the neck according as 

 there are present or absent certain stimuli connected with the acquisition 

 of food. In other words, there are two possible forms in which the 

 proportions of the neck would not vitally aflfect locomotion. One is 

 the anguilliform or eel-like type, which might be attained by elongation 

 of the body and tail without the length of neck being aflfected. No 

 living mammal swims by this method. The long-tailed zeuglodonts 

 were definitely modified in this direction and the neck was not elongated. 

 The other type of body referred to above is that in which the legs of one 

 side are separated from those of the opposite side by a relatively wide 

 interval. If this were the original body form, as it likely was in the 

 hippopotamus, we would expect all four legs to be employed in rapid 

 swimming, as is the case in the mud turtle, the ultimate probability being 

 that four paddles of approximately equal size would be developed, and 

 these could perform all functions of swimming and steering, permitting, 

 as far as locomotive factors are concerned, either the lengthening or 

 shortening of the neck. The size of the head in Hippopotamus might 

 be expected to inhibit the development of a long neck. The only other 

 mammalian instance for discussion under this head is the platypus. Its 

 body is now somewhat turtle-shaped, and may always have been so, for 

 all four feet are well developed for swimming. The fore feet are now 

 chiefly used for this purpose, which was permitted by the development 

 of an excellent equilibrating organ from the tail. Theoretically it could 

 now undergo a lengthening of the neck, which at present is short; but 

 it would seem that a short neck is advantageous to its habits of feeding. 

 It will occur to the reader that the duck employs somewhat similar 

 methods of feeding and it has a long neck, but this is a necessity for 

 proper equilibration in flight. If it were not then it would not be held 

 in an extended position, but curved as in the heron. 



Most of the aquatic mammals listed are not sufficiently specialized for 

 us to tell whether the length of neck is different from that of their an- 



[139] 



