140 EEPTILIA. 



the dorsal vertebrae, and are more numerous than those of the 

 caudal vertebrae. In the true Serpents, there are always above 

 100 vertebrae, usually above 200, or 300, as in the great Boas, while 

 the Python presents even 400 and upward, of which the caudal make 

 up only a fourth to a seventh part of the whole series. No traces of 

 a sternum are met with in the Ophidia. 



In the true Sauria the number of the vertebrae and ribs is also con- 

 siderable, being greatest in the elongated serpent-like forms of that 

 order, as Anguis, Pseudopus, Chirotes, Amphisbcena, where they 

 amount from 30 60 or 100, while that of the caudal vertebrae, 

 which at the extremity of the tail become very small and rudimentary, 

 frequently exceeds 100, as in Lacerta, Monitor, &c. The bodies 

 of the vertebrae, like those of the Ophidia, are generally concave 

 anteriorly, and provided with a hemispherical head posteriorly. 

 The cervical vertebrae, of which the second has an odontoid process, 

 are few in number, and generally devoid of ribs, but occasionally 

 support them ; to these succeed numerous dorsal vertebrae, and more 

 rarely behind them some lumbar vertebrae, e. g., in Monitor, Lacerta, 

 Chameleon, Draco ; lastly, a sacrum may be distinguished, usually 

 consisting of two vertebrae, with long transverse processes that unite 

 it to the iliac bones ; to the sacrum follow next the numerous caudal 

 vertebrae, frequently provided at their commencement with superior 

 and inferior spinous processes. Superior spinous processes are 

 usually found upon the cervical and caudal vertebrae, and upon the 

 latter, inferior processes also, forming at their root a hemispherical 

 canal, within which the aorta passes. Transverse and oblique 

 processes are likewise met with. The ribs are numerous, and 

 there are several anterior and posterior ones, as in the Lizards, 

 which are not connected to the sternum. In the Chameleon, the 

 broad body part of the sternum is merely cartilaginous, and the 

 costal cartilages, corresponding with the sternal ribs, coalesce to- 

 gether in the middle line, so as to form so many intersecting bands. 

 In the Flying Drago (Draco viridis), the anterior ribs alone are 

 united with the sternum ; the posterior, especially the three middle 

 ones, are very long and straight to support a membranous expansion, 

 which serves the animal as a parachute, to sail through the air 

 with from tree to tree. Nearly all the Saurians, with very few ex- 

 ceptions, such as AmphisboBna, possess a sternum, which occurs, 

 however, in a rudimentary condition in the other serpentoid genera. 

 It consists, as is well exemplified by the genera Lacerta, Monitor, 

 &c., of an anterior slender T-shaped or cruciform bone, which 



