GENERAL CHARACTERS. 



395 



and anterior surfaces, by which (with the intervention of cartilages) 

 it articulates with the adjacent centra, may be nearly flat or con- 

 cave, when it is said to be amphicoelous (fig. 815); or its anterior 

 surface may be more or less hollow, and the posterior convex (fig. 

 816), when it is termed procotlous ; or, lastly, the reverse of the lat- 

 ter arrangement may obtain, when the centrum is termed opisthoccel- 

 ous ; an example of the latter structure being shown in the vertebra 

 of Calamospondylus given in the sequel (fig. 107 1). Immediately 

 above the centrum is the 

 aperture of the channel for 

 the reception of the spinal 

 cord, known as the ?ieural 

 canal (fig. 816); this canal 

 being enclosed laterally and 

 superiorly by the neural 

 arches, which are surmounted 

 by the neural spine (figs. 815, 

 816). The lateral portions 

 of this arch are termed the 

 pedicles (fig. 817, n), and the 

 parts connecting the latter with the spine the lamina. The arch, it 

 should be observed, always ossifies separately from the centrum, 

 and the line of junction between the two when, as in many Rep- 



Fig. 816. — Anterior (b) and posterior (c) views of a 

 proccelous dorsal vertebra of a Lacertian Reptile 

 \l~aranus). The part above B and c is the centrum; 

 the aperture the neural canal, above and round which 

 are the neural arches, surmounted by the neural 

 spine ; the oblique facets are the zygapophyses, and 

 the lateral prominences the transverse processes, 

 which are here very short. 



Fig. 817. — a, Oblique anterior view of the lumbar vertebra of a Whale, b, Diagrammatic trans- 

 verse section of the bones of the thoracic region of a Mammal. Greatly reduced, rt, Prezyga- 

 pophyses ; b, Sternum ; c, Centrum ; d, Transverse process ; n, Pedicle of arch ; p, Sternal rib ; 

 r, Rib; s, Neural spine. (After Owen.) 



tiles, they remain distinct, is known as the neuro-central suture. 

 The neural arch bears a pair of processes, or facets, at either ex- 

 tremity for articulation with the adjacent vertebrae ; those at the 

 anterior extremity (fig. 816, b) being known as prezygapophyses, and 



