108 



Basic Structure of Vertebrates 





Fig. 105. Squalus vulgaris, Risso. (A) Dorsal fin and portion of the vertebral 

 column; four anterior (at left) vertebrae are cut in sagittal section, (ac) Anterior 

 cartilages (either modified radials or neural spines) ; (6c) basal cartilage : (c) centrum ; 

 (ca) calcified cylinder; (df) dorsal fin; (ha) hemal arch; (in) interdorsal cartilage; 

 (iv) intervertebral ligament; (li) dorsal ligament; (na) neural arch; (nt) notochord; 

 (r) radial cartilage; (sp) fin spine, with base cut away to expose cartilage core. The 

 cartilage is dotted. (B) Calcified cylinder of a centrum. (From Goodrich: "Studies 

 on the Structure and Development of Vertebrates." By permission of The Macmillan 

 Company, publishers.) 



the structure as a whole, being made possible by the inherent elasticity 



of all of the vertebral materials. Since bone is rigid, a bony vertebral 



column must have joints. 



Bony vertebrae bear various projecting processes, most of them 



serving for attachment of muscles. 

 Most constant are a pair of trans- 

 verse processes projecting laterally 

 from the sides of the centrum (Fig. 

 103). A second pair of transverse 

 processes may project laterally from 

 the lower region of the neural arch. 

 Also, there are usually accessory 

 articulating processes, zygapophy- 

 ses, consisting of a pair of prezy- 

 gapophyses projecting forward from 

 the anterior face of the neural arch 

 and articulating with a pair of post- 

 zygapophyses projecting backward 

 from the posterior face of the neural 

 arch of the adjacent vertebra (Figs. 



103, 104). Other processes, less common in occurrence, may be present 



on either the centrum or the neural arch. 



Fig. 106. Diagrammatic sections 

 of elasmobranch vertebrae. (A, B) 

 Cyclospondylous. (C) Asterospondyl- 

 ous (Courtesy, Kingsley: "Compar- 

 ative Anatomy of Vertebrates," 

 Philadelphia, The Blakiston Com- 

 pany.) 



