THE FOOT 653 



fits within the hoof, with its toe slightly lower than its heels (see 

 Fig. 219). 



The Foot-Joint. — Three bones form the foot-joint (Fig. 220). The 

 question naturally arises why the joint is not composed of two bones 

 instead of three, and what advantage is gained by the introduction of 

 a small dense bone, such as the navicular, into the articulation. The 

 articulation furnished by the pedis is much smaller than that pro- 

 vided by the corona, but by the introduction of the navicular, the 

 pedis plus navicular surface is nearly, but not quite, equal to the 

 corona surface. One use of the navicular bone is to increase the 

 articular surface of the pedis. But it is conceivable that this small 

 articular surface of the pedis might have been increased in some 

 other way than by the introduction of a distinct bone and other 



Fig. 219. — The Wall partly removed in order to show the Position of — 

 (1) The Pedal Bone ; (2) the Extent of the Lateral Cartilage. 



The dotted line through the latter indicates the portion within and without the 

 hoof. In the figure the cartilage has curled in and shrunk a little from 

 exposure. It will be noted that the pedal bone is lower in front than behind. 



complicated apparatus, and it is evident that the value of the 

 navicular articulation does not depend entirely on the fact that it 

 increases the size of the joint, but that it supplies what elsewhere 

 has been spoken of as a yielding articulation (see p. 609). The use 

 of this yielding articulation saves direct concussion. During locomo- 

 tion, when the foot comes to the ground, the weight through the 

 corona falls in the first instance largely on the navicular, which under 

 its influence yields slightly in a downward direction ; from the navic- 

 ular the weight is transferred almost entirely to the pedis, which 

 also yields slightly under its influence, and in this way direct concus- 

 sion to the joint is prevented. 



The Navicular Bone and Bursa. — The navicular would be of very 

 little use for the above purpose, if it depended on being kept in 

 position solely by the delicate ligaments which have origin from it. 



