42 THE SURGICAL ANATOMY OF THE HORSE 



portion of which is termed the transverse ligament. Through the 

 notch, and over the transverse ligament, the pubio-femoral ligament 

 passes to its insertion into the triangular sulcus in the head of the 

 femur. The ligamentum teres, or round ligament, is inserted superiorly 

 in the roughened portion of the acetabulum. 



In the floor of the pelvis there is formed, in each innominate bone, a 

 large foramen, which in outline approaches the elliptical. Its long axis 

 is directed forwards and slightly outwards. Anteriorly it is bounded by 

 the pubic bone and posteriorly by the ischium. This is the thyroid, or 

 obturator foramen, which in the recent state is almost completely closed 

 by a sheet of fibrous tissue, to which the name obturator membrane 

 is given. A small aperture is left anteriorly, and through this the 

 obturator vessels and nerve leave the pelvic cavity and descend to the 

 thigh. 



For descriptive purposes it is usual and convenient to take the 

 segments of the innominate bone separately. 



The Ilium. — Of the three portions into which the innominate bone 

 is divided this is the largest, and from a surgical point of view it is the 

 most important. The bone is of irregular shape and extends upwards 

 and forwards from the acetabulum, or what has been indicated in our 

 superficial examination as the position of the hip joint. The upper 

 portion of the ilium is flattened from above to below, and therefore 

 expanded in the lateral direction. The inferior portion is " narrow and 

 prismatic," and this part is frequently referred to as the shaft. 



Three surfaces may be described. The upper surface looks up- 

 wards, outwards, and backwards. It is widest superiorly and becomes 

 very narrow towards its inferior end. The upper portion is slightly 

 depressed and is smooth. This part accommodates the middle or great 

 gluteus muscle. Inferiorly the surface is convex and roughened, and 

 this portion presents a number of roughened ridges from which the 

 deep gluteus muscle arises. This is the gluteal surface. The sacral 

 or pelvic surface is so called since in part it bounds the pelvic cavity. 



