2o6 



COMPARATIVE ANATOMY 



addition to the two main spinal curvatures, thoracic and lumbar, man 

 also has two lesser curvatures, cervical and sacral, in the region of the 

 neck and sacrum respectively. 



Fig. i6o. Fig. i6i. 



Fig. i6o. — Diagrams of [A and B) fish vertebrae and (C) vertebra from higher 

 groups, b, basal stumps; c, centrum; ch, capitular head of rib; d, diapophysis; ha, hemal 

 arch; hr, hemal rib; n, notochord; na, neural arch; p, parapophysis; r, rib; t, tubercular 

 head. (From Kingsley's "Comparative Anatomy of Vertebrates.") 



Fig. i6i.— Two caudal vertebrae of alligator, c, centrum; ha, hemapophysis; hs, 

 hemal spine; na, neurapophysis; ns, neural spine; poz, prz, post- and prezygapophyses; 

 t, transverse process. The arrow passes through the neural arch. (From Kingsley's 

 "Comparative Anatomy of Vertebrates.") 



The Vertebral Column in Man. In the backbone of a child there are 

 thirty-three vertebral elements. During growth the last nine fuse to form 

 two adult bones, the sacrum and the coccyx. The other twenty-four 



c D 



ARTICULAR PROCESS INTERVERTEBRAL CARTILAGE 

 i CENTRUM I SPINOUS PROCES^ 



Fig. 162. — Diagrammatic sagittal sections of (A), amphicoelous; (B), procoelous; 

 (c), opisthocoelous; and (D), amphiplatyan vertebrae; the head is supposed to be at the 

 left. Cut surfaces obliquely lined. (After Kingsley modified.) 



vertebrae remain separate throughout life and become differentiated into 

 seven cervical vertebrae, twelve dorsal or thoracic, and five lumbar. 

 These are sometimes called "true" vertebrae in contra-distinction from 

 those of the sacrum and coccyx which are called "false" vertebrae. 

 Although the vertebrae are separate bones, they are nevertheless so firmly 

 fastened together by ligaments and fibrous cartilages as to make the 



