14 



SECTION I. 

 BONES. 



GENERAL CONSIDERATIONS OF BONE. 



The bones oi" the skeleto72 are two hundred and eleven in number, 

 of which twenty-two belong to the head, fifty-six to the trunk, sixty- 

 nine to the superior and sixty-four to the inferior extremity ; when 

 held together by ligaments and cartilages they form a natural skeleton, 

 when by other means an artificial skeleton. They are hard, white, 

 and inflexible; and more numerous in childhood than in old age. 



They are classified into long, thick, and flat bones. The body or 

 shaft of a long bone is called Diaphysis ; its articulating extremities. 

 Epiphyses; its processes and projections are called Apophyses. The 

 smaH foramina on the surface of bones are for the transmission of 

 nutritious vessels, the largest of which enters about the middle. 



Bones are composed of two structures, compact and cellular, which 

 are external and internal. The cells communicate with each other 

 and contain marrow. The compact structure consists of small fibres 

 arranged in laminsB ; each of these fibres has a canal running through 

 its length called the canal of Havers, transmitting vessels ; it commu- 

 nicates with small lenticular excavations called corpuscles of Pm'kinje, 

 by radiating tubes. The cellular structure increases the strength 

 without increasing the weight, and also diminishes the effect of con- 

 cussion. 



Composition of Bones, — Bones are chemically composed of animal 

 and earthy matters, united in the proportion of two parts of earthy 

 to one of animal, or, more accurately, consist of thirty-two parts of 

 gelatine, one part of insoluble animal matter, fifty-one parts of phos- 

 phate of lime, eleven of carbonate of lime, two offluate of lime, one 

 of phosphate of magnesia, and one of soda and muriate of soda ; the 

 earthy matter is most abundant in bones of the cranium ; the ani- 

 mal matter in the cellular structure. Combustion will remove the 

 animal matter, and dilute acids will remove the earthy matter. 



The Periosteum is a fibrous membrane investing the external sur- 

 face, adhering less firmly in infancy, and becoming ossified in old 

 age. It is vascular, insensible in health, assists in the secretion 

 of the external laminae, restrains ossification within proper limits, re- 

 ceives the insertion of muscles, tendons, &c. &c., and protects the 

 bone fi'om suppuration in the vicinity. 



