THE SKELETON 



61 



os innominatum, Oc, on each side, which is firmly fixed dorsally to 

 the sacrum and meets its fellow in the middle ventral line. In the 

 child each os innominatum consists of three bones, viz., the ilium, 

 the ischium, and pubis. Where these three bones meet and finally 

 ankylose there is a deep socket, the acetabulum, into which the 



FIG. 33. The skeleton of the trunk and the limb arches seen from the front. 

 C, clavicle; S, scapula; Oc, innominate bone attached to the side of the sacrum 

 dorsally and meeting its fellow at the pubic symphysis in the ventral median line. 



head of the thigh-bone fits (see Fig. 17). Between the pubic and 

 ischial bones is the largest foramen in the whole skeleton, known as 

 the doorlike or thyroid foramen. The pubic bone lies above and 

 the ischial below it. The ilium forms the upper expanded portion 

 of the os innominatum to which the line drawn from Oc in Fig. 33 

 points. 



