16 GUIDES FOR VERTEBRATE DISSECTION 



centrum for nearly its whole length. (In carefully prepared 

 specimens dia- and pleurapophyses contain cartilages with which 

 the ribs articulate, but usually these are lost.) The horizontal 

 lamina is perforated by the foramen ventrale (for the collateral 

 vertebral vessels), which passes, posterior to the pleurapophysis, 

 to a deep pit, the posterior vertebral fossa, bounded by centrum, 

 transverse process, and postzygapophysis. 



The ribs are short, tapering somewhat distally, while proxi- 

 mally each is forked, presenting two surfaces, a dorsal tubercular 

 and a ventral capitular head, for articulation with dia- and para- 

 pophyses. 



Draw a vertebra and ribs from different sides showing these 

 points. 



Compare other vertebrae with this one. Where is the neural 

 spine largest? Do all bear transverse processes? Is the ventral 

 foramen present in all? 



The first vertebra is the atlas. What is the relative length 

 of its centrum? Is it amphiccelous? On its anterior surface are 

 a pair of slightly concave surfaces (condylar facets) for articula- 

 tion with the base of the skull. Does the atlas bear ribs? 



The vertebra with which the hind legs are connected (by 

 means of the pelvic girdle) is the sacrum. Could the element 

 intervening between this vertebra and the pelvic arch be con- 

 sidered as a rib? Has it two heads? Counting the atlas as 1, 

 what is the number of the sacrum in your specimen? Compare 

 with other skeletons in the laboratory; is the numerical position 

 of the sacrum constant? 



Study the caudal vertebrae. On what one does an arch 

 (haemal arch) on the ventral side, comparable to the neural arch, 

 appear? Is there a disappearance of parts towards the tip of 

 the tail? Are transverse processes constant throughout the 

 series? Are ribs present on any of the caudal vertebras? How 

 many caudal vertebrae are present? 



(Sternum. Wilder has described cartilages in the ventral 

 body wall, unconnected with other parts, which are regarded as 

 sternebras, or sternal elements. They are lost in skeletons pre- 

 pared in the ordinary way.) 



The Skull is composed of two parts, the cranium, containing 

 the brain and special sense-organs, and the visceral skeleton, 

 connected with the alimentary tract. In the cranium, in turn, 



