340 



THE CAT. 



[CHAP. x. 



each limb diverges from the others to a certain extent. The hallux, 

 however, does not continue to develope. At first each limb is so 

 placed that its dorsal surface is outwards, and thus the concavities 

 of both the elbow and knee are directed inwards. As development 

 proceeds, the two limbs are both rotated, but in opposite directions. 

 The fore-limb becomes so rotated that the extensor surface is turned 

 backwards, while the pelvic limb is rotated so that the correspond- 

 ing surface is turned forwards. Thus, the elbow and knee come to 

 be bent in opposite directions. The pelvic limb requires no further 

 torsion, since the foot is now ready to assume the posture needful 

 for locomotion. The bent arm, however, would have the back of 

 the fore-paw turned downwards if no farther change took place a 

 posture manifestly inconsistent with the animal's mode of walking, 

 which requires the palmar surface to be applied to the ground. 

 This difficulty is obviated by a further torsion, but one which is 

 confined to the forearm and paw. This further torsion consists in a 

 change from the primitive condition of supination into that before 

 described aspronation. "With the exception of the clavicle, all the 

 bones of the fore-limb are preformed in cartilage. 



In the scapula the coracoid process shows a separate centre of 

 ossification, and two such appear in the acromion process. The 

 supra-spinous part of the scapula ossifies as a separate plate of bone, 

 and is quite distinct from the rest at birth. 



The Jmmenis arises from one main ossification in the shaft, and 

 two terminal epiphyses. The proximal epiphysis arises from three 

 centres, one in the head and one in each tuberosity. The distal 

 epiphysis arises from four centres, which respectively appear in the 

 two condyles, the capitellum and the trochlea. Both the radius and 

 the ulna ossify from one central ossification in the shaft, and two 

 terminal epiphyses. 



Ossification of the carpus begins later than does that of the meta- 

 carpus and digits ; only one centre of ossification is formed in each 

 carpal, except the scapho-lunar, which has two. 



The first, or most pre-axial metacarpal (that of the pollex), has 

 its epiphysis at its proximal end. The epiphysis of the other meta- 

 carpals is placed at the distal end of each. All the phalanges 

 without exception have their epiphyses at their distal ends (Fig. 60). 



The ossification of the lower limb begins soon after that of the 

 upper, a bony nucleus appearing early in the shaft of the femur, and 

 also in that of the tibia. Apart from the patella, all the bones of 

 the pelvic limb ossify from cartilage. 



The os innominatum arises from three centres those of the ilium, 

 ischium and pubis with certain epiphyses, the principal of which 

 are one on the tuberosity of the ischium and another along the 

 crest of the ilium. 



The femur (Fig. 6) has one epiphysis for its head, one for each 

 trochanter and one for its distal end. 



The tibia and fibula have each one principal ossification that of 

 the shaft and two terminal epiphyses. In the tibia the superior 



