_O.il._, Ilium; _O.p._, pubis; _O.is._, ischium; _A.o.i._, wing of ilium; _C.o.i._, shaft of ilium; _Cr.o.i._, anterior border (crest) of ilium; _1_, obturator foramen; _2_, acetabulum; _3_, internal angle of ilium; _4_, external angle of ilium; _5_, gluteal line; _6_, psoas tubercle; _7_, _8_, acetabular and symphyseal branches of pubis; _9_, _10_, acetabular and symphyseal branches of ischium; _12_, lesser sciatic notch; _13_, ischial arch; _14_, great sciatic notch; _15_, symphysis pelvis; _17_, ilio-pectineal eminence; _18_, anterior borders of pubic bones; _19_, posterior gluteal line. (Struska, Anat. d. Haustiere.) ] The =pelvic surface= (Facies pelvina) faces in the opposite direction; it is convex, and consists of two distinct parts. The inner triangular part (Pars articularis) is roughened for ligamentous attachment, and bears an irregular facet, the =auricular surface= (Facies auricularis), for articulation with the sacrum. The outer quadrilateral part (Pars iliaca) is in general smooth. It is crossed by the =ilio-pectineal line= (Crista iliopectinea), which begins below the auricular surface and is continued on the shaft of the bone to join the anterior border of the pubis. The line is interrupted by furrows for the iliaco-femoral vessels, and below these it bears the =psoas tubercle= (Tuberculum psoadicum), which gives attachment to the psoas minor muscle. The iliacus muscle is attached to the surface external to the ilio-pectineal line. The =anterior border= or =crest= (Crista iliaca) is concave, thick, and rough. The =internal border= is deeply concave; its middle part forms the lower boundary of the =great sciatic foramen=, and it is continuous behind with the =superior ischiatic spine=. The =external border= is concave and in great part rough. Its fore part is crossed by grooves for the ilio-lumbar vessels, which are continued on the pelvic surface. The =nutrient foramen= is usually situated on or near the posterior part of this border. [Illustration: FIG. 61.—OSSA COXARUM OF MARE, VENTRAL VIEW.