84f OSTEOLOGY. 



animals than in man, where, especially in the female, it is large 

 and well developed, possessing that peculiar basin-like form 

 identified with an erect posture of the body. We have already 

 described the sacrum and coccyx, and have now to describe the 

 ossa innominata, or right and left segments of the pelvis. 



OSSA INNOMINATA. 



The ossa innominata are flat, but somewhat irregularly-shaped 

 bones, which form the sides, floor, and part of the roof of the 

 pelvic cavity. Above they are connected with the sacrum, and 

 below united to each other in the adult by ossification. In the 

 young animal, as above stated, and especially in the foetus, each 

 os innominatum consists of three parts, which retain their names 

 of ilium, ischium, and pubis, even after union by ossification. 

 They all three meet in the acetabulum, or articular cavity for the 

 femur. 



ILIUM. 



(PL. I. U.) 



The ilium, the largest and most symmetrical bone of the three, 

 and situated partly upon the sacrum with which it articulates, is 

 flat and irregularly-triangular in shape, its extreme outer angle 

 being one of the most prominent points of the animal, forming the 

 projection commonly called the " point of the hip." It presents 

 for consideration two surfaces, three borders, and three angles or 

 processes. 



The external surface is concave at its upper part, and marked 

 by elevated lines for the attachment of the gluteus maximus 

 muscle ; lower down it becomes convex and narrow, forming the 

 upper part of the shaft of the ilium, which is three-sided. As it 

 approaches the acetabulum the shaft again slightly expands, and 

 becomes roughened for the attachment of the gluteus internus and 

 outer head of the rectus femoris muscles. This surface terminates 

 in an obtuse angle, the outer side of which forms a strong 

 anterior margin for the acetabulum ; and the inner side, surmount- 

 ing this cavity, marks the line of junction between the ilium and 

 the ischium. 



The internal or venter surface is slightly convex, its upper 

 portion consisting of two parts an outer smooth one, correspond- 

 ing to the iliac fossa in man ; and an inner, which rests on the 



