THE INNOMINATE BONE 45 



apex of this angle forms the highest portion of the skeleton in the region 

 of the croup. The remaining angle is the inferior extremity of the 

 bone, and this is the portion which meets the ischium and the pubis 

 in the cotyloid cavity. Almost immediately in front of the cotyloid 

 cavity we find two small pits. They are placed one on either side 

 the cotyloid edge of the bone, and in them the tendons of origin 

 of the outer and inner heads of the rectus femoris muscle are 

 attached. 



Connecting the angle of the croup with that of the haunch, we have 

 the crest of the ilium. 



The ischium, in size, is the second largest of the three constituent 

 parts of an innominate bone. It is placed posteriorly, is flattened from 

 from above to below, and may be said to present, for the purposes 

 of description, two surfaces, four edges, and four angles. The superior 

 surface is very slightly depressed and forms the posterior part of the 

 floor of the pelvis. It is smooth, and upon it the urethra rests. The 

 inferior surface is almost flat and is slightly roughened. To this 

 surface the tendons of origin of the adductor muscles of the thigh 

 are attached. 



The anterior border is curved and forms the posterior boundary 

 of the obturator foramen. The posterior edge is also curved, and 

 is directed downwards and inwards. With the corresponding edge of 

 the opposite ischium it forms the ischial arch. The outer edge is 

 likewise curved. It is smooth and rounded, and forms the inferior 

 boundary of the lesser sacro-sciatic foramen. Across this border the 

 common tendon of the obturator internus and pyriformis muscles passes 

 to obtain insertion in the trochanteric fossa of the femur. The inner 

 edge meets the corresponding edge of the opposite bone, forming the 

 ischiatic symphysis. 



The antero-internal angle meets the posterior angle of the os pubis. 

 The antero-external angle enters into the formation of the cotyloid 

 cavity where it meets the os pubis and the ilium. The postero-internal 



