436 



THE RABBIT. PHYLUM CHORDATA 



known as an os innominatum or os coxa. With the sacrum it 

 forms a ring called the pelvis. In each os coxae may be recognised 

 a large dorsal ilium articulated with the sacrum, a posterior 

 ischium, and a smaller, ventral and anterior pubis which unites 

 with its fellow in a symph^^sis or fusion. The ischium and pubis 

 are separated by a large obturator foramen, above and below 

 which they meet. Above the obturator foramen all three parts 



Radius 



Fibula. 



Olecranon 

 process, 



Ulna. 



Head of ulna, 

 front new. 



Cnemlai 

 crest. 



Tibia. 



Fig. 347. — A, Elbow joint of left fore-limb of rabbit, outer view ; B, head of right 

 ulna of rabbit, seen from in front ; C, right tibia of rabbit, from in front. 



of the OS innominatum are continuous around the acetabulum, 

 a hollow into which the head of the femur fits. 



The hmbs contain bones for each of their segments ; a humerus 

 in the brachium and a femur in the thigh ; a radius and an ulna 

 in the forearm and a tibia and a fibula in the shank ; several 

 carpals in the wrist and tarsals in the ankle ; metacarpals in the 

 metacarpus and metatarsals in the metatarsus ; and a bone, not 

 distinguished by name, in each phalanx of each digit (Fig. 331). 

 The nomenclature of the carpals and tarsals is confused and 

 difficult, and this and other points about the limb skeleton are 

 discussed more fully on page 556. 



The limbs of tetrapods originally stuck out horizontally at 

 right angles to the body, and the surface which in the rabbit 



