ELEMENTAR Y ANA TOMY. [LESS. 



LESSON II. 



THE SKELETON IN GENERAL, THE INTERNAL SKELETON, 

 THE BACKBONE, BREASTBONE, AND RIBS. 



i. THE word " SKELETON" 1 is popularly taken to denote 

 only the bones, or at most the bone and gristle which form 

 the internal support of the body. 



An acquaintance with other animal structures, however, 

 shows that this signification is far too restricted ; for parts 

 which are bony in man 'may be cartilaginous (i.e. of gristle) 

 or even merely membranous, in other animals ; and conversely, 

 parts sometimes quite external, which are merely fibrous in 

 man, may be horn or bone, or contain bones and cartilages, 

 in other animals. 



The nature and structure of fibrous tissue, 2 of cartilage, and 

 of bone, have been sufficiently described in the first and twelfth 

 lessons of the " Elementary Physiology." It may, then, here be 

 shortly stated that the word skeleton, in its widest and most 

 scientific sense, should include not only the bones and car- 

 tilages, but also those fibrous structures (or membranes) which 

 surround such bones and cartilages, and thence radiating 

 invest every organ of the body, and finally clothe it externally 

 in the form of skin. 



The whole skeleton, then, may be denoted by the term 

 Fibro-chondr-osteal 3 apparatus. 



Fibrous tissue indeed penetrates the very bones them- 

 selves, and supports the marrow they contain ; it separates 

 each muscle from its neighbour, and surrounds and lines every 

 tube and passage in the body ; so that if every other tissue 

 could be dissolved away and yet this fibrous tissue be left, 



1 Derived from a-at \/\to, to dry. 



2 Each kind of substance of which the body is composed is termed a /issue. 

 Thus we speak of fibrous tissue and of osseous tissue or bone, also nervous 

 tissue, &.c. 



3 Because partly fibrous, partly cartilaginous, and partly osseous. 



