52 SKELETON. 



have their shapes diversified by muscular connexion and by the 

 forms of the viscera they contain. The thick bones (ossa 

 crassa) are situated in the vertebral column ; and in the hands 

 and feet ; and have their surfaces very irregular. 



The bones present, on their periphery, eminences and cavi- 

 ties, a proper knowledge of which, is of the greatest importance 

 to the surgeon. The former are called apophyses or processes, 

 and are extremely numerous and diversified: they serve for the 

 origin and insertion of muscles, and for furnishing articular 

 faces. The cavities are also numerous : some of them are su- 

 perficial, and serve for articular surfaces; others for the origin 

 of muscles; for the enlargement of other cavities, as that of the 

 nose and ear ; and for purposes which will be mentioned else- 

 where. 



The articular ends of the long bones are called epiphyses, 

 from their being formed from distinct points of ossification, 

 whereas, the shaft of the bone is its diaphysis or body, being 

 the part first formed. The epiphysis, therefore, as its name 

 implies, grows upon the other. Many processes grow after 

 the manner of epiphyses, from distinct points of ossification, 

 though they are seldom called by the same appellation. This 

 is the case with the trochanters of the os femoris, with the pro- 

 cesses of the vertebra, the crista of the ilium, and the tuber of 

 the ischium. 



Near the centre of some bones a canal is formed which passes 

 in an oblique direction, and transmits blood vessels to their in- 

 terior. There are also, at the extremities of the long bones, at 

 the different points of the thick ones, and near the margins of 

 the flat ones, a great many large orifices, which principally 

 transmit veins: in addition to which, a minute inspection of any 

 bone whatever, will show its whole surface studded with still 

 smaller foramina, also for the purpose of transmitting blood 

 vessels. 



The density of bones is always well marked, and exceeds 

 much that of other parts of the body. It is, however, variable 

 in different bones, and in different places of the same bone: 

 hence their substance has been divided into compact and .eel* 

 lular, of which the former is external and the latter internal. 



The cellular structure, or substance, grows from the internal 



