NECTUIIUS MAOULATUS. 



391 



vertebrae at the sacrum, aud but three at the first haemal arch. The results of countiua' 

 the vertebrae iu 100 specimens are expressed bv Bumpus in the following table: — 



No. of vertebrae. No. of specimens. 



43 9 



100 

 By tliis it will be seen that the average total number is 45 or 46. 



A Typical Vertebra. 



In order to understand the structure of the separate vertebrae, any trunk vertebra 

 except one of the first two or three may be selected as a type and its parts studied in 

 detail, after whicli the differences seen in other regions may be noted, and a few special 

 vertebrae selected as worthy of individual study. The 16th vertebra has been selected 

 for this purpose, and four views are given of it in text figures 1-4. These figures were 

 drawn from a dried vertebra prepared l)y macer- 

 ation in caustic potash and hence lack the cartilag- 

 inous portions and other related soft parts referred 

 to in the text. 



This vertebra consists primarily of a ventrally 

 situated centrum or body; a neural arch, the dorsal 

 aspect of which is broadened out into a Ijroad, flat 

 plate ; and upon each side a complicated transverse 

 process directed backwards and bearing a short rib 

 which articulates with it in two places. 



The centrum is in the form of a slender hour 

 glass, its ends marked by very deep cup-shaped 

 depressions, thus making the entire vertebra con- 





Fig. 1. lijtli vertebra ; dorsal aspect. X 3. 



