THE LOWER EXTREMITY. 125 



The phalanges of the third row are the smallest ; on 

 the anterior surface of the distal extremity they present 

 the elliptical pulp plates, rough surfaces which support 

 the pulp. The distal phalanx of the thumb is the 



largest. 



THE LOWER EXTREMITY. 



THE OS INNOMINATUM. 



The os innominatum, an irregular bone, forms, with 

 its fellow, the anterior and lateral walls of the pelvis. It 

 develops in three separate pieces, which become solidified 

 into one bone at about the twentieth year. 



The upper portion is called the ilium ; the anterior 

 portion, the pubes; the inferior portion, the ischium. 



The ilium is the broad, flattened, and expanded por- 

 tion of the bone ; the two ilia form the false pelvis, and 

 support the abdominal viscera. 



The ilium presents for examination an outer and 

 inner surface, a superior border or crest, an anterior and 

 posterior border. The outer surface looks outward, down- 

 ward, and backward. It is smooth, convex in front, 

 concave behind, and is marked by three curved lines, the 

 superior, middle, and inferior. The superior is short, be- 

 gins about an inch anterior to the posterior superior spine, 

 and curves downward and backward. The middle curved 

 line begins about an inch behind the anterior superior 

 spine, and terminates near the great sacro-sciatic foramen. 

 The inferior curved line begins near the anterior inferior 

 spine, and terminates near the lower part of the great 

 sacro-sciatic foramen. Below the inferior curved line is 

 a depression for the attachment of the reflected tendon 

 of the rectus. 



The inner surface is bounded above by the crest, an- 

 teriorly by the anterior border, posteriorly by the posterior 

 border, and below by a prominent ridge called the ilio- 



