FUSION OF CKRVICAL VERTEBRAE 



351 



developed supra-occipital in the adult. Here again the Zeuglo- 

 donts are more typically Mammalian, for in them the parietals 

 have a normal development and situation, rising even into a 

 median crest as in so many quadrupeds. The bones related 

 to the organ of hearing, the tympanies and petrous hones, are 

 very solid and dense in structure. Moreover they are but 



ExO 



Fig. 185. — A section of a skull of a young Caa'ing Whale (Globicephalus melas). x |. a, 

 Angle ; an, anterior nares ; AS, alisphenoid ; bh, basiliyal ; BO, basioceipital ; BS, 

 basisphenoid ; al, condyle ; cp, corouoid process ; JixO, exoccipital ; Fr, frontal ; 

 id, inferior dental canal ; IP, interparietal ; ME, ossified portion of the meseth- 

 moid ; Mx, maxilla ; A'a, nasal ; Pa, parietal ; Per, periotic ; PI, palatine ; PMx, 

 premaxilla ; pn, posterior nares ; PS, presphenoid ; Pt, pterygoid ; s, symphysis 

 of mandible ; sh, stylohyal ; SO, supra-occipital ; Sq, squamosal ; th, thyrohyal ; 

 Vo, vomer. (From Flower's Osteology.) 



loosely attached to surrounding bones, and are thus easily and 

 frequently lost. Nearly the only mammals which resemble the 

 Whales in the fact that the pterygoids sometimes meet in the 

 middle line below are the Edentata (Anteater and Armadillo, see 

 p. 167). But in both groups this peculiarity is not universal. 



The vertebral column is remarkable for the fact that more or 

 fewer of the cervical vertebrae may be fused together into a short 

 and compact mass. This is seen at its maximum in the genera 

 Balaena and Mohalaena. The odontoid process of the second 



