140 



ANIMAL BIOLOGY 



original form is only a temporary structure, being partially or 

 completely replaced during later development by a linear series of 

 cartilaginous or bony elements, known as vertebrae, which form 

 the vertebral column, or backbone. This is one of the most 

 characteristic structures of Vertebrates as compared with Inverte- 

 brates, or backboneless animals. (Figs. 94, 95, 100.) 



A typical vertebra of the higher animals consists of a basal 

 portion, known as the centrum, and a neural arch which it 

 supports. These form a protecting ring of bone about the spinal 



Scapula 



Clavicle 



Procoracoid 



Glenoid cavity 

 Humerus 



Pubis 



Coracoid 



Radius— 



I-Ulna 



Intermedium 



Radiale {] 



Two centralia^Opt^--" Ulnare 

 Five distalia -TJ^> C> O 



7t°q£ 



Five metacarpals _///? II \l 



n in 



Ischium 



— Fibula 

 Intermedium 



Tibia — 



Tibiale^UL^- 



^OQO— Fibulare 

 Five distalia ——p* qq a 



n£Q Qr 



Five metatarsals -J / I [j 



Phalanges - 



I 



" III 



Fig. 102. — Diagram of the plan of the Vertebrate limbs. A, fore limb and 

 pectoral girdle; B, hind limb and pelvic girdle. (From Hegner, after Parker 

 and Has well.) 



cord. From various parts of the vertebra as a whole arise proc- 

 esses for movable articulation with its neighbors, the attachment 

 of muscles, etc. Between the vertebrae of the Mammals are 

 cushions of cartilage which absorb shock. (Fig. 101.) 



In some forms, rirs are attached to the transverse processes of 

 certain vertebrae. These extend outward and downward within 

 the body wall, and usually are attached in the ventral line to the 

 breast bone (sternum). Thus, in the adult of the higher Verte- 

 brates, the series of centra of the vertebrae come to occupy the 

 position formerly held by the notochord; while above, the neural 



