OS INNOMINATUM. 



Fig. 163. Plan of the Development of the Hand. 



227 



Alt cartilainous 



Metacarpus 



2 Centres for euch Tione 

 -if or Shctfe- 



1for Digital Extremity 

 except 14- 



Phalanges 



2 Centres for each lone 

 If or Shaft 



xtv. 



the third and fourth years, and a year later in those of the second and third 

 rows. The two centres become united in each row, between the eighteenth and 

 twentieth years. 



OF THE LOWER EXTREMITY. 



The Lower Extremity consists of three segments, the Thigh, Leg, "and Foot, 

 which correspond to the arm, forearm, and hand in the upper extremity. It is 

 connected to the trunk through the os innominatum, or .haunch, which is 

 homologous with the shoulder. 



THE Os INNOMINATUM. 



The Os Innominatum, or nameless bone, so called from bearing no resem- 

 blance to any known object, is a large irregular-shaped bone, which, with its 

 fellow of the opposite side, forms the sides and anterior wall of the pelvic 

 cavity. In young subjects it consists of three separate parts, which meet and 

 form the large cup-like cavity, situated near the middle of the outer side of 

 the bone ; and, although in the adult these have become united, it is usual to 

 describe the bone as divisible into three portions the ilium, the ischium, and 

 the pubes. 



The Ilium, so called from its supporting the flank (ilia), is the superior broad 

 and expanded portion which runs upwards from the upper and back part of 

 the acetabulum, and forms the prominence of the hip. 



The Ischium (io&ov, the hip) is the inferior and strongest portion of the bone ; 



