76 THE SKELETON OF THE CAT 



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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 coxae 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, d), 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 (/). 



Fig u — iNNOMi- Caudad of the acetabulum are two bars. 



NATE Bone OK Kit- The dorsal one of these is the ischium (//), 



ERAL \^Eur'"^^''' and the ventral one is the pubis (///). The 



/, ilium; //, ischium; ischium enters into the formation of the 



Srone-^^r'aSl acetabulum (a), but the pubis does not. 



ulum ; (^, obturator fora- fhc two boucs, however, are in contact at 



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 (d). 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 (/V). 

 In the adult cat these four parts are united into a single bone 

 which is nevertheless usually described, ignoring the acetabular 



