DESCRIPTIVE AND SURGICAL 



ANATOMY. 



OSTEOLOGY-THE SKELETON. 



T 



HE entire skeleton in the adult consists of 200 distinct bones. These are 



The spine or vertebral column (sacrum and coccyx, included) 26 



Cranium 8 



Face 14 



Hyoid bone, sternum, and ribs 26 



Upper extremities . . . . 64 



Lower extremities 62 



200 



In this enumeration the patellae are included as separate bones, but the smaller 

 sesamoid bones and the ossicula auditus are not reckoned. The teeth belong to 

 the tegumentary system. 



These bones are divisible into four classes : Long, Short, Flat, and Irregular. 



The Long Bones are found in the limbs, where they form a system of levers, 

 which have to sustain the weight of the trunk and to confer the power of locomo- 

 tion. A long bone consists of a shaft and two extremities. The shaft is a hollow 

 cylinder, contracted and narrowed to afford greater space for the bellies of the 

 muscles ; the walls consist of dense, compact tissue of great thickness in the middle, 

 but becoming thinner toward the extremities ; the spongy tissue is scanty, and 

 the bone is hollowed out in its interior to form the medullary canal. The 

 extremities are generally somewhat expanded for greater convenience of mutual 

 connection, for the purposes of articulation, and to afford a broad surface for 

 muscular attachment. Here the bone is made up of spongy tissue with only a thin 

 coating of compact substance. The long bones are not straight, but curved, the 

 curve generally taking place in two directions, thus affording greater strength to the 

 bone. The bones belonging to this class are the clavicle, humerus, radius, ulna, 

 femur, tibia, fibula, metacarpal and metatarsal bones, and the phalanges. 



Short Bones. Where a part of the skeleton is intended for strength and com- 

 pactness, and its motion is at the same time slight and limited, it is divided into a 

 number of small pieces united together by ligaments, and the separate bones are 

 short and compressed, such as the bones of the carpus and tarsus. These bones, 

 in their structure, are spongy throughout, excepting at their surface, where there 

 is a thin crust of compact substance. The patellae also, together with the other 

 sesamoid bones, are by some regarded as short bones. 



Flat Bones. Where the principal requirement is either extensive protection 

 or the provision of broad surfaces for muscular attachment, we find the osseous 

 structure expanded into broad, flat plates, as is seen in the bones of the skull and 

 the shoulder-blade. These bones are composed of two thin layers of compact tissue 

 enclosing between them a variable quantity of cancellous tissue. In the cranial 

 bones these layers of compact tissue are familiarly known as the tables of the 



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