18 ANATOMY. 



with the carpals, and the large one below with the first phalanx 

 and the sesamoids. The small metacarpals are comnionly known 

 as splint bones. 



The iirst phalanx is commonly known as the pastern. It is 

 the shortest bone in the body that is classified as a long bone. 

 The shaft shows an anterior, convex surface and a posterior sur- 

 face which is flattened and rough. The upper extremity is marked 

 by two shallow cavities, separated by a median groove and fitted 

 for articulation with the two convex surfaces and the median 

 ridge which mark the inferior extremity of the large metacarpal. 

 The lower extremity has two articular surfaces separated by a 

 median groove like that of the large metacarpal. 



The sesamoids are two small, somewhat triangular, and irreg- 

 ular bones, placed side by side just back of the upper part of the 

 pastern bone. These articulate with both the large metacarpal 

 and first phalanx or pastern. They are side by side and together , 

 form a groove for the flexor tendons. 



The second phalanx, or coronet bone, is short and somewhat 

 square in form. It articulates with the first phalanx above, and 

 the third phalanx and navicular below. The upper and lower ex- 

 tremities of this bone resemble the upper and lower extremities 

 of the first phalanx. 



The third phalanx, or pedal bone, is pyramidal in shape and 

 irregular. Its superior face shows two shallow cavities separated 

 by a median ridge fitted for articulation with the second phalanx. 

 The anterior face is convex and quite rough. Tiie inferior sur- 

 face is the one on which the foot rests. It is called the sole. 

 The superior border of the anterior face has quite a projection 

 which is especially fitted for the insertion of a tendon. This is 

 technically known as the pyramidal process. The lower portion 

 of this bone is continued outward and backward on each side into 

 what is known as the wing. 



The navicular bone is located just back of the upper part of 

 the third phalanx and is articulated to that bone. It is long and 

 narrow, and i)laced transversely. Its anterior surface articulates 

 with the third phalanx. Its posterior surface is covered with 

 cartilage and forms a gliding surface for the tendon of the deep 

 flexor muscle which passes over this bone to its attachment on 

 the sole f)r inferior surface of tlic third phalanx. 



