44 ANATOMY AND PHYSIOLOGY. 



and layer is superadded upon layer, until the necessary degree of 

 thickness is obtained. In the round bones, ossification proceeds 

 from the centre to the circumference. In the long bones, ossifica- 

 tion commences at the middle of the shaft, and extends outward 

 gradually till near the ends, where it stops. At a period soon after 

 birth, the ends of the long bones begin to ossify separately, at their 

 centre, in the same way that the short bones do, and they continue 

 separated from the shafts of the bones by a layer of cartilage, till 

 the 15th, 16th, or even 18th year. Hence children should on no 

 account be rudely pulled about, or twisted about the limbs, as the 

 ends of the bones are apt to be twisted off, producing incurable 

 lameness. 



The most common affection for which we have to treat bones, is 

 their fracture. Most of the bones when broken unite in three 

 weeks, if properly kept at rest, but the thigh-bone is never fit for 

 walking upon in less than six. 



The following list exhibits the number of bones in the several 

 regions of the body. 



The Spine contains . . . .24 



Pelvis, ..... 5 



Breast-bone, .... 1 



Ribs, . ' .'^ . .-/. : .; r 24 



Arms, ... . - . 64 



Legs, ... V . 60 



Head, . . . . V 22 



Total, .'- --.. ' . 200* 



RECAPITULATION. 

 BONES OF THE HEAD. 



Frontal Bone. Situated in the anterior part of the skull, forming 

 the forehead and upper part of the orbits. 



Parietal Bones. Situated one on each side of the superior part 

 of the cranium. 



Occipital Bone. Situated in the posterior part of the cranium. 



Sphenoid Bone. Situated in the middle of the basis of the 

 cranium, extending underneath from one temple across" to the 

 other. 



Temporal Bones. Situated at the sides and inferior part of the 

 cranium. 



* Douglas. 



