POSTERIOR ARCH. 



325 



three bones of each os innominatum unite at one point towards 

 the posterior part of the pelvis, forming a concavity called the 

 acetabulum (5). The ischium on each side lies against the 

 sacrum, to which they are attached by muscle. Into the 

 acetabulum or cotyloid cavity fits the head of the thigh-bone 

 or femur, forming a ball-and-socket joint similar to the one 



Fig. 188. — Pelvic Arch. (Seen from below.) 



1, Iliac surface ; 2, auricular facet ; 3, crest of ilium ; 4, angle of haunch ; 5, cotyloid 

 cavity ; 6, bottom of ditto ; 7, one of the imprints for the insertion of the rectus femor- 

 alis ; 8, ileo-pectineal line ; 9, channel on the external face of pubes ; 10, obturator 

 foramen ; 11, sciatic spine ; 12, ischiatic arch. (Chauveau.) 



at the junction of the fore-limb and arch. The femur is a 

 thick solid bone with a large smooth head, at the side of which 

 is developed a large roughened projection called the ti-ochanter 

 major. About one-third of the way down the bone is a swell- 

 ing or tuberosity found only, fully developed, in Solipeds (Horses, 

 &c.) — namely, the third trochanter — to which are attached vari- 



