CHAPTER VIII. 



THE SKELETON. 



THE word skeleton is used in a broader and in a narrower 

 sense. In the broader sense it comprises all those tissues which 

 are developed for the support and protection of the rest, and 

 which form the framework of the essential parts of the various 

 organs. These are, in the main, connective tissue, cartilage, 

 and bone. Were it possible by some subtle solvent to dissolve 

 out all the tissues but connective tissue, we should still have a 

 perfect model of the vertebrate body in this material. Bone 

 and cartilage are more restricted in position. They may be 

 said to constitute the skeleton in the narrower sense in which 

 it is used in this chapter ; while the dried skeleton is composed 

 of bone alone. 



The skeleton may be divided into the following parts : 



I. Axial Skeleton 



1. The skull and branchial arches. 



2. The vertebral column, ribs, and sternum. 



II. Appendicular Skeleton 



1. The pectoral arch and fore-limb. 



2. The pelvic arch and hind-limb. 



The Skull. The skull, into the composition of which there 

 enter certain elements derived from the branchial arches, is 

 developed : (1) for the protection of the brain ; (2) for the 

 lodgment and protection of the special sense-capsules ; and (3) 

 for the support and attachment of the jaw-apparatus. The 

 olfactory (o/.), optic (op.\ and auditory (au.) capsules always 



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