186 MS. H. a. SEELEY ON OSSEOUS BESEMBLANCES 



PAET III. 



THE SIMILITUDES OF LIZABD BONES. 



§ 1 . The Mammalian Characters of Lizards. 



The nearest approximation to the diverging V-shaped parietal 

 crest of Lizards is the faint V-crest of certain Seals, like the 

 Grrey Seal. The few mammals which have the external nostrils 

 double never have the division made by the nasal and premaxil- 

 lary bones meeting mesially, but by a jutting forward of the 

 ethmoid. The maxillary bone is similarly excluded in Euminants 

 and Pachyderms from a circumscribed orbit, by development of 

 the malar and lachrymal bones. 



A change in the forms of the teeth, like that of many Lizards, 

 is seen in many mammals in the transition of incisors to canine, 

 and to premolars and molars ; only the molar teeth of Lizards 

 never have a divided fang. 



The ribless neck-vertebrse in the Monitor are six ; in other 

 Lizards there are usually fewer. Oxen have a strong neural 

 spine and a well-developed hypapophysis ; but neither is rela- 

 tively ever so long as in the Monitor ; and mammals never have a 

 long intervertebral ossicle as in Iguana, or a procoelous cup-and- 

 ball articulation ; in many of the long-necked mammals the 

 transverse process is as little developed as in Lizards. The axis 

 of Iguana, with its large forward-reaching neural spine, and large 

 odontoid process placed immediately under the neural canal, 

 might well be compared to a mammal's. In long-necked mam- 

 mals like the Griraft'e there is a similar obliquity in the articula- 

 tion in the centrum, its upper part leaning forward. 



The dorsal vertebrae agree with those of all mammals except 

 Cetaceans in not having the ribs supported on transverse pro- 

 cesses, though a few early vertebree in the Dragon have a short 

 massive lateral process to which the large head of the rib arti- 

 culates. They resemble Mynnecophaga and Cetacea in having 

 the rib attached only to its own proper vertebra. They resemble 

 true Whales in the articulation being strictly single, but differ 

 in the expanded cup-shaped articular head, which is sometimes 

 vertical. This single-headed condition is seen in the hinder ribs 

 of many mammals and in OrnithorliyncTius. 



The dorsal region has the visceral surface of the centrum 



