218 THE ANATOMY OF VEETEBEATED ANIMALS. 



the tail, that appendage is pretty certain to part at one of 

 these weak points. 



The arches of the vertebrae of the Lacertilia are articulated 

 together by the ordinary oblique processes, or zygapophyses. 

 In the Iguance they are additionally connected by a process 

 of the front part of each arch {zygosphene), which fits into 

 a fossa on the posterior face of the preceding arch (zygan- 

 trwm). These Lacertilian vertebrae thus nearly approach 

 the vertebrae of the Ophidia. 



The transverse processes of the vertebrae are very short, 

 and are, at most, divided into two indistinct facets, with 

 which corresponding facets on the proximal ends of the ribs 

 articulate. 



Ribs may be developed in all the cendcal vertebrae except 

 the atlas, and they usually increase in length towards the 

 dorsal region, where more or fewer of them become con- 

 nected with the sternum. The dorsal moiety of the primi- 

 tive cartilage of the rib becomes ossified, and the primitive 

 cartilage bone is finally replaced by membrane bone. The 

 ventral moiety becomes converted only into cartilage bone, 

 and may pass directly and withoxit articulation, on the one 

 hand into the sternum, and on the other into the vertebral 

 rib. Processes are sometimes developed from the posterior 

 margins of certain of the ribs, which are termed processus 

 uncinati. The sternum, when fully formed, consists of a 

 rhomboidal anterior portion, from the posterior angle of 

 which a single, or double, backward prolongation is con- 

 tinued into the wall of the abdomen. Two or three pairs 

 of the sternal ribs are connected with the posterolateral 

 edges of the rhomboid, while the rest may be attached to 

 the abdominal prolongations ; or, behind these, they may be 

 continued into one another, to form complete hoops aci-oss 

 the wall of the abdomen (Geckos, Chamseleons, Scincoids). 



The Flying Lizard {Draco volans) is remarkable for the 

 elongation of naany of its posterior ribs, which are con- 

 tinued into, and support, the parachute-like expression of 

 the integument by which it is enabled to perform its 

 flights. 



