46 THE SURGICAL ANATOMY OF THE HORSE 



angle comes into apposition with the corresponding angle of the opposite 

 ischium at the symphysis, whilst the postero-external angle forms the 

 tuber ischii. This is a thick, roughened projection, the summit of which 

 may be readily located in the living animal by palpation, since it forms 

 the projection a few inches below and slightly to the side of the root 

 of the tail, which is not infrequently referred to as the point of the 

 hip. On the inferior aspect of the tuber ischii there is found a pro- 

 minent and well-defined ridge. This is the inferior ischiatic spine, and 

 to it the erector muscles of the penis are attached. 



The OS pubis is placed in front of the ischium and forms the anterior 

 portion of the floor of the pelvis. It is much the smallest of the three 

 component parts of the innominate bone, and in connection with it 

 there may be described two surfaces, three edges, and three angles. 



The superior surface is smooth and concave, and on the slight depres- 

 sion which it forms with the opposite bone, the urinary bladder rests. 

 The inferior surface is slightly convex, and is roughened for muscular 

 attachment. Running obliquely backwards and outwards across this sur- 

 face from the symphysis to the cotyloid cavity is a well-marked groove. 

 This is the pubio-femoral groove, and it derives its name from the 

 ligament which it accommodates and which is peculiar to the equidiP, 



The anterior border forms part of the brim of the pelvis. Towards 

 the pubic symphysis this edge is thin and sharp, but outwardly it 

 is roughened, thick, and tuberous. The inner edge comes into 

 apposition with the corresponding edge of the opposite bone, thus 

 forming the pubic symphysis. The remaining or outer border 

 is curved, the concavity of the curve being directed backwards and 

 outwards. This edge forms part of the anterior and inner boundaries 

 of the obturator foramen. 



The angles are termed antero-internal, antero-external, and posterior. 

 The first-named angle meets the corresponding angle of the opposite 

 bone at the symphysis. The antero-external angle enters the cotyloid 

 cavity, where it is articulated to the ilium and ischium. The posterior 



