ir. VERTEBItATA. 



517 



of human anatomy) enclose a spinal canal surrounding the spinal 

 cord, the parts of the aroh, neurapO'physes, uniting above the cord 

 to form the spinous process (frequent!}' an independent part of the 

 skeletal axis). In the caudal region, in the same way, luemal 

 arches may be formed of limnupo-pliyses and hcemal sjnne, the arches 

 surrounding the blood-vessels of the tail (fig. 557). In the trunk 

 region the ventral arch behaves differently. Since the large body 



Fig. 5r)6.— Vertebrae of sturgeon, ch, notochord;/, exit of nerve ; /, dorsal and ventral 

 intercalaria ; k, neural canal: o^^ neural arch; s, chordal sheath; v, rib; xlU, 

 htemal arch. Bone ^^hite, cartilage dotted. 



I'sPt 





Fig. 5.57. Fio. 558. 



Fig 557 — f'audal vertebra? of a carp, section (A) and nearly side view (Ji). rh space 

 filled by notochord; h, htemal arch: n, neural arch; ub, neural spme; mO, lia?mal 



Fig "•>")« —Thoracic vertebra, ribs, and sternum of a mammal. (From Wiedersheira.) 

 r„ capitular head of rib ; Co, neck of ril): Ci>, bony rib; Kn, cartilaKinous rib- /s, 

 spinous process; PU transverse process (diapophysis) ; .s'(, sternum; lb, tuber- 

 cular head of rib; U'A', vertebral centre. 



cavity with its viscera, varying in size (digestive and reproductive 

 organs), is here, the hajmapophyaes extend outwards and down- 

 wards and are divided into two ]iarts, a b:isal apophysis and a 

 lower movable portion, the ril (fig. 55G). Also the lower union 

 of hffiniapophyses with h»mal spine does not occur; the I'lbs are 

 either free (fishes) or are (at least in part) connected veutrally by 



