148 



CHORDATE ANATOMY 



skeleton is still cartilaginous, but the cartilage is often hardened with 



lime. 



Bony vertebrae make their appearance in ganoid fishes, some of 



which however retain a cartilagin- 

 ous vertebral column. Ball-and- 

 ^^^^^^ socket joints between the centra 

 are developed in Lepidosteus (gar- 

 pike) as in some Amphibia. Am- 

 phicoelous or biconcave vertebrae, 

 however, predominate in all groups 

 of fishes. Centra are wanting in 



Fig. 136. — Sagittal section of Sqaulas the Dipnoi, 



vertebrae, cut surfaces obliquely lined. ^-^j^ ^-^^ amphibians, bone 



c, calcifications of centra; cd, caudmeurals; _ ^ 



cdh, caudihemals; cr{i), cranineurals SUCCecds cartilage; and the VCrte- 



(intercalaria) ; d exits of dorsal nerve roots; ^^^^ ^^^ differentiated intO Cervical, 

 crh, cranihemals; n, notochord; v, exits or 



ventral nerve roots. (From Kingsley's trunk, Sacral, and caudal. The 



"Comparative Anatomy of Vertebrates.") ^-^g^^ ^^^^^^ vertebra is but slightly 



modified for attachment to the pelvic girdle. A single atlas represents 

 the cervical series of higher forms. Zygapophyses, for articulating each 

 vertebra with its two neighbors, first appear in this group. Articulation 



Fig. 137. Fig. 138. 



Fig. 137. — Diagrams of (.4 and B) fish vertebrae and (C) vertebra from higher 

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

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

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



Fig. 138. — 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.") 



with the ribs is effected by two sorts of processes, diapophyses from the 

 neural arches and parapophyses from the centra. 



Lumbar vertebrae are first differentiated in reptiles, which also have 

 two sacral vertebrae. Here also appear vertebrae with centra flattened 



