38 ELEMENTARY ANATOMY. [LESS. 



arch was permanently distinct from (i.e. unanchylosed with) 

 the centrum, and in the Carp the transverse processes are 

 separate. Even the neural arches may be made up of two 

 separate pieces on each side, as in Elasmobranch fishes, e.g. 

 Raia and Spinax. 



That degree of adjustment of parts which exists in each 

 vertebra of man is not universal. Thus, e.g., we find in the 

 Tortoises neural arches- so shifted as to be respectively 

 annexed to* two centra, and thus the intervertebral foramen 

 comes to be placed opposite the middle of each vertebral 

 body. 



A similar displacement takes place in the upper parts of 

 the divided neural arches of the Elasmobranchs just referred 

 to, so that the parts are united by a zigzag suture. 



c 



FIG. 48. AXIAL LONGITUDINAL ECTION OF THE VERTEBRAL COLUMN OF AN 

 ELASMOBRANCH (Raia). 



c, one of the centra which, being bi-concave, forms lozenge-shaped sections by its 

 junctions with the concave surfaces of adjacent vertebral centra; s,.a. neural 

 spine ; 2 > one f tne dorsal parts of a neural lamina ; n lt one of the ventral 

 parts of a neural lamina. 



20. The NUMBER of vertebrae in man is far less than exists 

 in most Vertebrates, though more than in some. No Verte- 

 brate has much less than a third his number even the Frogs 

 having ten. 



On the other hand, some sharks have more than eleven 

 times as many vertebras as man, and some serpents more even 

 than a dozen times his number. 



Man has the smallest number existing in his own class, 

 with the exception of some Bats and Monkeys. 



21. The division of the vertebras into the five CATEGORIES 

 of man's vertebral column is common to most forms above 

 Fishes, but we may find the lumbar vertebras indistinguish- 

 able and the sacral absent ; and in Fishes we can hardly 

 define even a single cervical, the vertebras being reduced to 

 but two categories, namely, those of the trunk and those of 

 the tail. 



