APPENDIX. 285 



maturity, through the ossifying or non-ossifying of the sutures, the 

 greater or less development of the processes for muscular attach- 

 ment, and the adaptation of the cranium to the size and shape of 

 the brain. The so-called "facial angle," formed by a line drawn 

 from the forehead to the most prominent part of the upper jaw, 

 and meeting a line from the middle of the ear to the base of the 

 nose, shows the difference in the form of the head, and is an index 

 to the intelligence of the several orders of mammals. 



In the skeleton of the horse, a careful study of the angle formed 

 by the scapula and humerus with that formed by the ilium and 

 femur, will show how antagonism in direction gives stability of 

 position. Were both angles directed the same way, the bones would 

 shut together and the animal fall. That there may be a double 

 antagonism and a lower against an upper, the angle formed by the 

 humerus and forearm antagonizes that formed by the femur and 

 leg ; hut each respectively in the contrary direction to the antago- 

 nism immediately above it, thus intensifying the stability. 



Comparing the anterior limbs of different orders of mammals 

 with those of birds, reptiles, and fishes (see Fig. 481) the same funda- 

 mental idea will be recognized in all, yet so modified as to adapt 

 the several species to the most diversified modes of life. Thus from 

 man to the fish are found the humerus (H), the ulna and radius of 

 the forearm (Ur), the carpal bones (C), the metacarpal (MC), and the 

 phalanges (PH). The greatest modification is observable in the wrist- 

 bones (indicated by the dotted line) and those below. The normal 

 number of carpals, metacarpals, and phalanges, is sometimes reduced 

 and sometimes multiplied, that the limb may be used specifically, 

 according to the wants of the animal, for swimming, crawling, fly- 

 ing, paddling, running, digging, climbing, etc. The perfection of the 

 human hand, which combines nearly all these uses, depends chiefly 

 on the free revolving motion of the humerus and the rotation of the 

 radius about the ulna. This mode of action necessitates a clavicle. 

 The more perfect this bone, the greater the power of rotating the 

 forearm ; and, when the clavicle is wanting, the radius and ulna are 

 usually consolidated and the forelimbs become only columns of sup- 

 port or instruments of progression. Tin's latter condition existing in 

 the horse and the ruminants, the metacarpals are greatly elongated, 

 elevating the heel to the height of the knee in other quadrupeds, 

 and permitting the toe only to touch the ground. 



The posterior extremities follow the analogies of the anterior in 

 most mammals, the true knee with its patella being more- or less 



