ANATOMY OF THE HORSE. 17 



fenioris ; to the inner side of and below the cavity is the obtura- 

 tor foramen, a large oval opening, closed by an expansion of 

 ligament, through the anterior part of which is a perforation for 

 the passage of the obturator vessels and nerves. Behind the 

 foramen the surface is broad, even, and smooth, and gives origin 

 to the abductor muscles of the thio-h ; above the foramen, it is 

 smooth but rounded, over which part play the obturator inter- 

 nus and gemelli. 



The Internal or Ventral Surface — Divided the same as the 

 external. The anterior part faces inwards and forwards, is 

 slightly and unevenly convex, has a superficial scabrous depres- 

 sion posteriorly, marking the place where the bone rests upon, 

 and has strong ligamentous attachment to the transverse pro- 

 cesses of the sacrum : the remainder of the surface below is 

 occupied by the iliacus, the part above being opposed to the 

 sacrun). — The posterior part is subdivided by a prominent border 

 (upon which is a rough mark showing the point of insertion of the 

 psoas parvus) into a small triangular superficial concavity, look- 

 ing forwards, which gives origin to the sartorius, and an exten- 

 sive but irregular one directed upwards; this last is much con- 

 sumed by the obturator foramen, posteriorly to which the surface 

 is remarkably smooth and slightly excavated for sustaining the 

 bladder. 



Anterior Border — Sigmoid in figure, slightly concave and thin 

 in the middle; terminating, behind, in a sharp salient angle, the 

 posterior iliac spine ; before, in a thick quadrangular part which 

 gives rise to four eminences: the two larger ones are the antero- 

 superior and antero-inferior iliac spines ; the two smaller, tubercles 

 or appendices to them. The border itself is called the crista 

 ilei. It affords attachment to the longissimus dorsi, obliqui 

 abdominis, externus et internus, and transversalis abdominis. 



Posterior Border — Having its anterior third thick and scab- 

 rous, where it is united through the intervention of fibrous car- 

 tilage with its fellow, forming the symphysis pubis ; posteriorly 

 to this, it grows thin, which part has also a ligamentous connec- 

 tion with the opposite bone, and afterwards recedes from its 

 fellow, terminating outwardly in a thick, oblong, waving, rough- 

 ened prominence, called the tuberosity of the ischium, to which 

 are attached the adductor magnus, biceps femoris, and abduc- 

 tor tibialis, and also the sacro-sciatic ligaments. 



The Superior Border — Extending from the posterior iliac spine 

 to the ischiatic tuberosity, is waving in its course, forming an ir- 

 regular semi-circle, and presents along its anterior two-thirds a 

 sharp edge, which opposite to the acetabulum is roughened by 

 the implantation of the sacro-sciatic ligaments ; after this it is 



D 



