ii.] THE SPINAL SKELETON. 23 



\ve should have a complete outline model, as it were, of the 

 entire human frame. 



Portions of this fibrous tissue which connect adjacent bones 

 and cartilages become very strong, and constitute the " liga- 

 ments " of the joints of the solid skeleton. 



2. The skeleton as a whole is naturally divisible into two 

 parts, to be separately treated of. 



(a) The external, peripheral skeleton, often called the EXO- 

 SKELETON, 1 the skin and its appendages. 



(ff) The internal, central skeleton, often termed the ENDO- 



SKELETON. 2 



The external skeleton will be considered afterwards. First 

 in order is the skeleton commonly so called, i.e. the internal 

 skeleton. 



3. The ENDOSKELETON of man is composed of numerous 

 bones, together with cartilages and fibrous structures. 



The number and nature of the solid parts vary with age. 

 In the earlier stages of existence there are no bones at all, 

 and the process of bone-formation (or ossification] having once 

 begun, goes on till the period of adult maturity is completed, 

 and indeed, to a less extent, throughout the whole of life. 



Thus it happens that parts which are membranous in the 

 baby or cartilaginous in the youth, become bony in the grown 

 man ; and a continuation of the same process tends to fuse 

 together more and more, bones which at their first appearance 

 were separate and distinct. 



Indeed, besides the coalescence of distinct bones, another 

 fusion of bony structures occurs. This is due to the fact 

 that the ends, or projecting portions, of what are essentially 

 and ultimate-ly one bone, arise as separate ossifications, which 

 are termed epiphyses? Thus the ends of the long bones of the 

 limbs are at first separate bones from the main part (or shaft) 

 of each long bone, and do not become continuous with the 

 shaft till near man's maturity. 



The hard parts of the internal skeleton being those which 

 as a framework support the body, form points of attachment 

 for the muscles which move it ; the muscles employing the 

 different bones like so many levers, or fulcra, as the case 

 may be. 



4. The great ma'ority of the bones are thus intended to 

 move one upon another, and the contiguous surfaces of such 

 movable bones form THE "JOINTS." 



1 From tf ID, without. - From ifv&ov, within. 



3 From ewi, upon, and <pvttv, to grow. 



