84 OUTLINES OF EQUINE ANATOMY. 



termed the venter. It is convex for tlie most part, and is 

 •divided into two portions by a roughened articulatory 

 surface for the transverse process of the first sacral bone. 

 This articular surface {auricular facet) looks obliquely 

 downwards and forwards, and is smoothest centrally, 

 where is sometimes found a small synovial cavity. Its 

 outer margin is very rough for attachment of the sacro- 

 iliac ligament. The surface anteriorly placed to this, which 

 )liel23S to form the brim of the pelvis, is triangular, termi- 

 jjating in a point inferiorly. It gives attachment to the 

 iliacus, and that portion of it which forms the anterior 

 l>art of the neck presents transverse grooves, through 

 which runs the arteria innominata from behind forwards 

 in its course to the triceps cruralis. This surface is sej^a- 

 a-ated from the posterior surface, which is much narrower, 

 and gives origin to pyriformis, by grooves running directly 

 •downwards to the obturator foramen, through which the 

 obturator vessels and nerve pass. In contact with this 

 surface superiorly and under the first sacral transverse pro- 

 cesses are the iliac arteries andtheir commencing branches, 

 also the external, internal, and common iliac veins. 



OS ISCHIUM occupies the postero -inferior part of the 

 pelvis, and consists of three processes with the body 

 at which they join. The antero-exiernal jjrocess runs for- 

 wards to help to form the acetabulum, consequently the 

 superior part of its anterior surface is roughened for 

 articulation with the ilium and its infero-anterior j^art for 

 union with os pubis. It is smooth, both externally and 

 internally ; externally, in forming the neck of the ischium, 

 over which obturator internus and pyriformis play, the latter 

 muscle is attached to a roughened line on the upper part of 

 Ihe process ; internally in forming with the ant ero -internal 

 process an arch with rounded margin, which looks forwards 

 and gives attachment to obturator externus, and assists in 

 forming the obturator foramen. The anterior extremity 

 of the last-mentioned process joins os pubis, while its inner 

 margin, meeting its fellow, assists the corresponding part 

 of the body in forming symphysis ischii, the union becom- 

 ing strengthened below by a connecting ligament, particu- 

 larly thick opposite the posterior margin of obturator 

 foramen, in becoming reflected down to form the triangular 

 ■ligament of the penis of the male. The superior margin of 

 (Symphysis pubis et ischii affords attachment along almost 



