VERTEBRATES. 297 



stant, but in the shoulder-girdle other bones may be added, 

 or either coracoid, or coracoid and clavicle may disappear. 

 In the birds the clavicles unite, forming the wish-bone 

 (furcula). 



The bones of the fore limb (fig. 107) are: a single bone 

 (humerus) in the arm; two bones (ulna and radius) side 



FIG. 107. Diagram of fore and hind limbs of a terrestrial vertebrate, with one 

 half of their girdles, c, carpus; cl, clavicle; co, coracoid; /.fibula; e, femur; 

 A, humerus; il, ilium; is, ischium; me, metacarpus; mt, metatarsus; p, 

 pubis; r, radius; s, scapula; t, tarsus; u (in upper) ulna, (in lower) tibia; 

 1-5, digits, each composed of phalanges. 



by side, in the forearm; a series of nine bones (carpals) 

 in the wrist; five longer bones (meta car pals) in the palm; 

 and several rows (phalanges) of five bones in the digits. In 

 the hind limb the conditions are closely similar: a single 

 femur in the thigh, tibia and fibula in the shank, nine 

 tarsals in the ankle, five metatarsals succeeding these, and 

 finally the phalanges of the toes. 



These are the typical numbers, but they may be reduced 

 through disappearance or fusion, and this reduction usually 

 appears first in the toes, and may proceed so far, as in the 

 horse, that one toe alone remains functional. 



The nervous system consists of a central and a periph- 

 eral portion, the latter consisting of nerves going from 

 the central system to all parts of the body. To these 

 should be added the organs of general and special sense. 



