14 TEE BONES. 



met with in the head and the upper regions of the Umbs. c. A bone which 

 offers nearly the same development in all its dimensions, is called a short bone 

 (example : the astragalus). Destitute, like the preceding, of a medullary canal, 

 the short bones are found in the spine and some regions of the limbs. 



B. Relative Form. — To make known the relative form of a bone, is to indicate 

 the greater or less exact resemblance it may bear to geometrical figures, or to 

 familiar objects. Thus, the scapula is a bone of a triangular shape. 



Regions of the Bones. — When describing the eminences and external 

 cavities of bone^ it is essential not to allude to them casually by passing 

 indifferently from one to another. To avoid the diificulties resulting from the 

 application of such an irrational system, it is necessary to divide the bone to be 

 studied into several regions, in which external peculiarities can be examined 

 successively, as they present themselves. The general course to be followed in 

 order to learn the regions of a long, a flat, and a short bone, is as follows : — 



a. A long bone is always divided into three parts — a body and two extremities. 

 The bod// or middle portion, or diaphysis, is the narrowest part of the bone. In 

 shape it is a geometrical solid, inclining somewhat to that of a very long prism. 

 On the body of a bone, therefore, there are studied as many faces and planes, 

 angles or borders, as on the prism it represents. 



The extremities, or epiphyses, are more or less considerable enlargements, 

 formed primarily by a special bony nucleus, and offering articular surfaces, as 

 well as surfaces for muscular or ligamentous insertion. 



b. A flat bone must necessarily have two faces, and borders and angles. 



c. A short bone has more or less faces, and plane or salient angles which are 

 often ignored, because of their trifling ijnportance. 



External Peculiarities of Bones. — These markedly attract the attention, 

 because they modify the general shape of bones, and singularly assist in 

 distinguishing one bone from another. These peculiarities, which are real 

 distinctive features that permit their description to be precisely established, are 

 always either eminences or cavities, according to their different uses. 



A. Eminences. — The eminences that stand out in relief from the surfaces 

 of bones, are divided into two different categories. One class concurs in the 

 formation of the articulations which join the bones to each other ; they are 

 named articular eminences, in which, again, are distinguished diarthrodial and 

 synarthrodial eminences, according as they belong to movable or immovable 

 articulations. The others, usually destined for the insertion of ligaments and 

 muscles, are called non-art icidar eminences or eminences of insertion. 



(The term imp-int is also used in anatomy, and signifies a collection of small 

 rugged eminences which make the surface of the bone uneven and rough. There 

 are muscular, tendinous, ligamentous, and aponeurotic imprints, according as 

 they give attachment to muscles, tendons, ligaments, or aponeuroses.) 



a. The synarthrodial eminences are always indentations more or less deep and 

 finely cut, which stud the border of large bones. 



b. The diarthrodial eminences are volimiinous, smooth, and in a fresh state 

 covered with cartilage. They are named heads and condyles : heads, when they 

 describe the segment of a sphere (head of the femur, head of the humerus) ; 

 condyles, when they represent an ovoid segment cut parallel to its larger axis 

 (condyles of the femur). 



c. The non-articular eminences receive various names. If they are volumi- 

 nous and much detached from the bone, they are called processes or apophyses. 



