30 



BULLETIN OF THE 



In Phoca and the earless seals generally no great sexual differences 

 in the structure of the pelvis appears to be known. From the great 

 breadth of the pelvis between the pubic bones in the male, no modifica- 

 tion of the male form of the pelvis would seem requisite in the female. 

 In the eared sen Is, however, especially in Callorhinus, the pelvis is 

 exceedingly narrow, especially anteriorly, in the males, and of small 

 capacity. In the females it is hence necessarily entirely open in front, 

 and the pubic bones and the ischia are reduced to a mere bony rim 

 enclosing the very large thyroid foramen. The ventral borders of the 

 innominate hones are also less produced. The more posterior position 

 of the acetabula in the eared seals places the hind limbs in a position 

 better fitting them to support the body, and hence for terrestrial locomo- 

 tion. They are, in fact, placed but little anterior to their position in 

 many of the true walking mammalia. 



The following table of comparative measurements indicates the differ- 

 ence in proportions and form of the pelvic bones in Phoca, Macrorhinus, 

 JSumetopias, Callorhinus, and Rosmarus : — 



Owing mainly to the great elongation of the very thick neck in the 

 Otariada, the fore limbs, as long since mentioned by Cuvier,* are ap- 

 parently placed much farther back than in the Phocid<z.\ 



The neural spines in Phoca are but slightly developed, especially an- 

 teriorly, whilst in Eumctopias and Callorhi)ins, as well as in Eos?narus, 

 they are largely developed, especially those of the anterior dorsal verte- 



* Oss. foss., Vol. V, j). 216. 



t By actual measurement they are found to be but little anterior to the middle of the 

 entire length of the animal. 



