THE ISCHIUM 107 
part of the ischiatic spine (Spina ischiadica), which is roughened laterally, smooth 
medially. Two depressions above and in front of the acetabulum give attachment 
to the tendons of origin of the rectus femoris muscle. This angle is connected with 
the wing or wide part of the bone by a constricted part, termed the shaft (Corpus 
ossis ilium). The latter is of three-sided, prismatic form. Its lateral surface is 
convex and rough, and gives attachment to the deep gluteus muscle. Its pelvic 
surface is smooth and is grooved for the obturator vessels and nerve. Its ventral 
surface is crossed by vascular grooves, below which there is a rough area, which is 
bounded medially by the psoas tubercle. 
Crest of ilium Tuber sacrale 
Tuber Gluteal 
core surface 
of ilium 
Ischiatic spine 
Acetabulum 
Obturator foramen 
Tuber ischit 
Ischial arch 
Fic. 86—Ossa Coxarum or Horse; Dorsat View. 
A, Wing; A’, shaft of ilium; B, acetabular, B’, symphyseal branch of pubis; C, body, C’, acetabular branch (or 
shaft), C”, symphyseal branch, of ischium; 1, gluteal line; 2, grooves for obturator nerve and vessels; 3, symphysis 
pelvis; 4, greater sciatic notch; 5, ilio-pectineal eminence; 6, pubic tubercle. Dotted lines indicate primitive separa- 
tion of three bones. 
THE ISCHIUM 
The ischium (Os ischii) forms the posterior part of the ventral wall or floor of 
the bony pelvis. It slopes a little downward and inward, but is practically hori- 
zontal in the longitudinal direction. The body of the ischium (Corpus ossis 
ischii) is irregularly quadrilateral, and may be described as having two surfaces, 
four borders, and four angles. 
The pelvic surface (Facies pelvina) is smooth and slightly concave from side 
to side. 
The ventral surface (Facies ventralis) is nearly flat, and is in great part rough- 
ened for the attachment of the adductor muscles. 
The anterior border forms the posterior margin of the obturator foramen. 
