402 



COLLEGE ZOOLOGY 



The body of a vertebrate may be divided into a head, neck 

 (usually), and trunk. In many species there is a posterior ex- 

 tension, the tail. Two pairs of lateral appendages are generally 

 present, the thoracic (pectoral fins, forelegs, wings, or arms) 

 and the pelvic (pelvic fins, hind legs). The limbs support the 

 body, are locomotory, and usually have other special functions. 



A general account 

 of the plan of struc- 

 ture of an ideal ver- 

 tebrate can be given 

 most clearly with 

 the aid of diagrams 

 showing longitudi- 

 nal and cross sec- 

 tions through the 

 body (Figs. 345- 

 346). As in Am- 

 phioxus, the nerve 

 cord (sp.c) is dorsal 

 but extends in front 

 of the end of the 

 notochord and en- 

 larges into a brain. 

 The notochord be- 

 comes invested by 

 the vertebrae (Fig. 

 346, en). The ccelom (coel) is large. The alimentary canal forms 

 a more or less convoluted tube (int) which lies in the body 

 cavity. The liver, pancreas, and spleen are situated near the 

 alimentary canal. In the anterior trunk region are the lungs 

 and heart. The kidneys (ms.nph) and gonads (gon) lie above 

 the alimentary canal. 



Integument (Fig. 347). — The outer covering of the verte- 

 brates is the skin, consisting of an outer ectodermal layer, thei 

 epidermis (Sc, SM), and an inner mesodermal layer, the dermis: 



cLao 



Fig. 346. — Transverse section through the trunk 

 of a vertebrate, en, centrum of vertebra; coel, ccelom; 

 crd.v, cardinal vein; d.ao, dorsal aorta; d.f, dorsal 

 fin; d.m, dorsal muscles; f.r, fin-ray; gon, gonad; 

 int, intestine; l.v, lateral vein; mes, mesentery; 

 ms.n.d, mesonephric duct ; ms.nph, mesonephros; 

 na, neural arch; p.n.d, pronephric duct; pr, peri- 

 toneum, parietal layer; pr', visceral layer; r, sub- 

 peritoneal rib; r', intermuscular rib; sp.c, spinal 

 cord; t.p, transverse process; v.m, ventral muscles. 

 (From Parker and Haswell.) 



