76 THE SKELETON OF THE CAT 
capsule. The joint is further strengthened by a double lateral 
ligament on each side. The two sesamoid bones at each joint 
are interconnected by a strong transverse ligament, and each 
is connected with the head of the metacarpal and the base of 
the first phalanx by a lateral ligament. 
Phalanges.—Between the phalanges the joints possess cap- 
sules, and each has a radial and an ulnar lateral ligament. 
VI. BONES OF THE PELVIC EXTREMITIES. 
Innominate Bones. Ossa innominata. (Os coxe BNA) 
(Figs. 54 and 55).—The two innominate bones articulate 
with the sacrum and extend thence caudoventrad and finally 
turn mediad and unite in the middle line, forming the symphy- 
sis pubis. They thus form an arch, the pelvic arch, pelvic 
girdle or pelvis, which is closed dorsad by 
the sacrum. 
In the middle of the lateral surface of 
each bone is a hemispherical depression, the 
acetabulum (Fig. 55, @), which receives the 
head of the femur. 
In the kitten each innominate bone is 
composed of three principal parts united by. 
sutures (Fig. 54). From the sacrum to the 
acetabulum is a’single bar, the ilium (J/). 
Fic. 54. — INNomt- Caudad of the acetabulum are two bars. 
naTE Bonz oF Kir- The dorsal one of these is the ischium (//), 
TEN, VENTROLAT- P : 
ERA. VIEW: and the ventral one is the pubis (///). The 
/, ilium; Z/, ischium; ischium enters into the formation of the 
po Se a te acetabulum (a), but the pubis does not. 
ulum; 4, obturator fora- The two bones, however, are in contact at 
re the ventral edge of the acetabulum. .From 
this point they diverge, but unite with one another again near 
the middle line and thus enclose an oval foramen, the obtura- 
tor foramen (4). Wedged between the ilium, ischium, and 
pubis at their point of junction and helping to form the ace- 
tabulum is a small irregular bone, the acetabular bone (/1’). 
In the adult cat these four parts are united into a single bone 
which is nevertheless usually described, ignoring the acetabular 
