OSTEOLOGY. 3 l 



THE SESAMOIDS. 



The sesamoids consist of two superior or large, and one inferior, 

 small or navicular bone. 



THE LARGE SESAMOIDS. 



These are two in number, lying side by side behind the superior 

 part of the first phalanx. Each one is pyramidal, and has an 

 anterior face articulating with the metacarpal, a posterior, smooth 

 for the gliding of tendons, a lateral face, a base and summit. 



They articulate with the metacarpal and first phalanx. 



THE NAVICULAR BONE. 



The small sesamoid bone lies behind the third phalanx, to 

 which it is attached. It is long transversely and narrow, and 

 shows a superior surface, articulating with the second phalanx; 

 an anterior surface, articulating with the third phalanx; an in- 

 ferior surface, a posterior border and two extremities. 



THE POSTERIOR EXTREMITY. 



This is divided into the pelvis, thigh, leg, and foot. 



THE PELVIS. 



The pelvis is a bony cavity containing the sexual organs and 

 termination of the internal tract. It is formed above by the 

 sacrum laterally, and below by the os innominata. 



The os innominata are two bones, each one composed of three 

 segments closely fused together. In early life the innominata 

 bones are separate, but they are completely joined as age advances. 

 They consist of three segments, the ilium, ischium and pubes. 



THE ILIUM. 



The ilium is flat and triangular, and corresponds internally to 

 the sides of the sacrum. It has two surfaces, three borders, and 

 three angles. The external surface is rough, the internal surface 

 shows an external smooth and internal rough portion, the auric- 

 ular surface for articulation with the ilium. The anterior border 



