26 



BULLETIN OF THE 



the whole length is in the former as 15 to 100; in P. vitulina as 17 to 

 100. The same proportion in respect to the caudal vertebrae is in the 

 former as 20 to 100 ; in the latter as 28 to 100.* The relative length 

 of the sternum to the spinal column is as 35 to 100 in the eared seals, 

 and as 28 to 100 iu Phoca vitulina, indicating in the latter the relative 

 shortness of the thorax as compared with the whole length of the animal, 

 and hence its eminently cetacean form. 



In regard to the skull, Turner t showed many years since that the eared 

 seals are distinguished from the others by important cranial differences. 

 He compares them as follows : In the earless seals " there is no trace of a 

 postorbital process, nor of an ali-sphenoid canal; the mastoid can scarcely 

 be said to constitute a process ; it is swollen, and appears to form a por- 

 tion of the auditory bulla, more or less connected with the tympanic por- 

 tion, from which it is separated by a depressed groove running from the 

 stylo-mastoid foramen backwards and a little inwards. The paroceipital 

 process is never large in any of the family, but it is always distinctly de- 

 veloped and salient backwards. The Arctocephaline group are distin- 

 guished at once by their having a distinct postorbital process and an ali- 

 sphenoid canal ; the mastoid projects as a strong process, and seems, as it 

 were, to stand aloof from the auditory bulla." In Phoca and in other 

 types of the Phocidce, the bulla is many times greater than in the Otari- 

 adce, its increa.^ed size being doubtless compensatory for the absence of 

 an external conch. In the latter the occipital and sagittal crests in old 

 age attain an enormous development, which only a few of the higher 

 forms of the Phocidce at all approach. 



Considerable differences are also found in the form of the different 

 bones of the extremities of the two types. In the anterior extremities, 

 these consist in the reduced size and structurally low form of the scapula 

 in Phoca, *as compared with Eumetopias and CaUorhinus t (Figs. 12, 13, 



* In E. Slelleri as 15 to 100; in C. ursinus as 23 to 100; in the latter there being a 

 greater development of the post sacral vertebra;. 



t Proc. Lond. Zoul. Soc., 1848, p. 84. 



J The general form of the scapula in these groups (including Rogmnrus and Macro- 

 rhinus) is indicated by the following table: — 



