288 THE PELVIC GIRDLE. [chap. 



muscle of the leg. The pubic border (pb) is slightly 

 marked, constituting the tinea arcuata interna, or tinea ilio- 

 pectinea of human anatomy. The ischial border (ib) is 

 short and deeply hollowed. The acetabulum (a) is large, 

 circular, with very prominent borders, incomplete only for a 

 small space on the infero-internal aspect. 



The pubis and ischium are short, and widely divergent 

 from each other, so that the thyroid foramen (t/if) is elon- 

 gated in the direction across the main axis of the bones. 

 The symphysis (s) is rather short, and formed by the 

 pubis alone. Each of the apposed surfaces of bone is 

 capped by a plate of nbro-cartilage ; these are held to- 

 gether by strong ligamentous fibres, while between them 

 there is usually a more or less perfect synovial cavity. 

 Ankylosis at this spot, so common in the lower Mammalia, 

 very rarely takes place in Man. 



The posterior and inferior border of the ischium is thick- 

 ened and rounded, and distinguished as the tuber ischii (ti). 

 Above this, on the hinder border of the same bone, is a 

 smooth, hollowed surface, called the lesser sciatic notch, 

 surmounted by an angular prominence called the spine; 

 above the spine the edge of the ischium passes into the 

 great concavity of the posterior or ischial border of the 

 ilium, and which is called the great sciatic, or, more pro- 

 perly, ilio-ischiatic notch. The strong ligaments (sacro- 

 sciatic) which pass from the side of the pseudo-sacral and 

 caudal vertebrae, the one to the tuber and the other to the 

 spine of the ischium, convert these notches in the living 

 body into foramina. 



The anterior or superior (in the vertical position) outlet of 

 the pelvis is subcircular, usually rather broader from side to 

 side than from the vertebral to the pubic border. Its plane 

 is not far from a right angle with the axis of the vertebral 



