110 THE SKELETON OF THE HORSE 
bones are not fused until the second year. The epiphyseal parts fuse with the 
main mass at four and a half to five years of age. 
The acetabular part of the pubis ossifies from a separate center. It is most distinct in the 
embryo at three months, and is often called the os acetabuli. Martin says that the ilium has a 
center for the acetabular part, one for the shaft and wing, and a third for the crest. He also 
states that there is a special center for the acetabular part of the ischium, and a transitory nucleus 
in the symphyseal part of the pubis. 
THE PELVIS 
The bony pelvis is composed of the ossa coxarum, the sacrum, and the first 
three coccygeal vertebrae. The dorsal wall or roof is formed by the sacrum and 
first three coccygeal vertebrie, and the ventral wall or floor by the pubic and ischial 
Sacral Tuber 
Crest of ilium spines — sacral Tuber coxe 
Pelvic surface of 
ilium 
Lateral border of 
ilium 
Nutrient foramen 
Psoas tubercle 
Depression in which 
tendon of rectus 
femoris is attached 
Acetabulum 
TIlio-pectineal eminence — 
—— Tuber ischii 
ae, TIschium 
Pubic tubercle 
Fic. 88.—Petvic Bones or Marg, VIEWED FROM IN FRONT AND SOMEWHAT FROM BELOW. 
1, Body of first sacral segment; 2, surface on wing of sacrum for articulation with like surface on transverse process 
of last lumbar vertebra; 3, wing of sacrum; 4, sacro-iliac articulation; 5, sacral canal; 6, promontory; 7, apex of sac- 
rum; §, ilio-pectineal line; 9, ischiatic spine; 10, grooves for ilio-lumbar vessels; 11, grooves for iliaco-femoral vessels. 
bones. The lateral walls are formed by the ilia and the acetabular part of the 
ischia. The defect in the skeleton here is supplied in the fresh state by the sacro- 
sciatic ligaments and semimembranosus muscles. 
The anterior aperture or inlet of the pelvis (Apertura pelvis cranialis) is bounded 
by the terminal line (Linea terminalis) or brim, which is composed of the base of 
the sacrum dorsally, the ilio-pectineal lines laterally, and the pecten pubis ventrally. 
It is almost circular in the mare, semi-elliptical in the stallion, and faces obliquely 
downward and forward. It has two principal diameters. Of these, the con- 
jugate or sacro-pubic diameter (Conjugata anatomica) is measured from the sacral 
promontory to the anterior end of the symphysis. The transverse diameter 
