134 ELEMENTS OF COMPARATIVE ZOOLOGY. 



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. 60) are : a single bone 

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

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

 wrist; five longer bones (metacarpals) 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 peripheral 

 portion, the latter consisting of nerves going from the cen- 

 tral system to all parts of the body. To these should be 

 added the organs of general and special sense. 



The central system consists. of an anterior brain, passing 

 behind into the spinal cord. The brain is contained in the 

 cranium, the spinal cord passes through the tube formed by 

 the neural arches of the vertebrae. 



The spinal cord is somewhat cylindrical, tapering behind, 

 and contains in its centre a 

 small canal. Nerves arise from 

 the cord in pairs in regular se- 

 quence, and pass out between the 

 FIG. 6i.-DiagTammatic section vertebra to all parts of the body 



^^g^nu^f^T^K and to the limbs - Each of th ^ 

 nerve-root ;u<, white matter. spinal ner veS has two places of 



origin (roots) from the cord one near the dorsal, the other 



