ANTAGONISM OF THE MEMBRAL SEGMENTS. 91 



B. Tlie two scapulje vpitli the clavicles and the coracoid bones are commonly regarded 

 as constituting a sort of belt — the scapular arch or shoulder girdle. 



% 213. Pelvis— Pelvic Girdle— (Fig. 51).— This limla girdle is 

 complete in the cat. Each lateral piece — Os innominatum — is at- 

 tached to the sacrum bv its dorsal end, and ventrad joins its 

 platetrope (fellow of the opposite side) at the symphysis pubis. 

 The rounded vertebral end of each os innominatum is the Crista 

 ilii., and the caudal end is the ischiatic tuberosity. 



% 214. Shoulder and Hip Joints. — These are the proximal arthra 

 of the arm and the leg respectively, forming their points of attach- 

 ment vpith the shoulder girdle and the pelvis. Both are baU-and- 

 socket joints, but the former is the more free, and the position of 

 the entire joint may be changed on account of the suspension of 

 the scapula in the muscles. 



§ 215. Elbow and Knee. — These are both hinge joints, the lat- 

 ter being less encompassed by bone, and hence somewhat the freer 

 of the two. At the knee the femur articulates with the tibia only, 

 while the elbow is between the humerus and both the ulna and 

 radius. 



§ 216. Wrist and Ankle.^The latter is a true hinge joint, but 

 the former combines features of the hinge and the ball-and-socket 

 varieties. 



§ 211. The Bones of the Limbs. — All of these have been named 

 in the Introduction in connection with the description of Pig. 6 

 (§§ 82-85), and some wiU be described hereafter with more detail. 

 Reference will be made here only to certain general features of the 

 larger bones, and to the attitudes of the entire limbs. 



Antagonism of tJie Membral Segments. — It will be noted that, 

 excepting the distal segments, the corresponding segments of the 

 limbs point in opposite directions, and that the same antagonism 

 exists between the principal elements of the scapular arch and 

 the pelvic girdle. As a necessary concomitant, any two successive 

 segments, excepting in the case of the manus and antebrachium, 

 point in opposite directions. 



Prom this relation of the segments there are two results : Pirst, 

 that the weight of the body rests upon columns which are not only 

 near its opposite ends, but also tend to counteract each other for the 

 most part, so that stability is more easily maintained. Neverthe- 

 less, by exception, the distal segments coincide in direction, so that 

 both limbs may strike the ground in one direction, and thus propel 



