THE STUDY OF TEE BONES. II 



B. Relative situation to the other parts of the skeleton. To indicate the 

 situation of a bone, considered from this point of view, is to make known the 

 place it occupies in the region to which it belongs, and the connections it may 

 have with adjoining regions. Thus the radius is situated in front of the 

 ulna between the arm-bone and the carpus. 



Direction. 



This is absolute or relative. The direction of a bone may be vertical, 

 horizontal, or oblique. Example : the scapula is placed in an oblique direc- 

 tion from above to below, and from behind to before. 



Configuration of the Bones. 



FORM. This is also absolute or relative. 



A. Absolute Form. The absolute form of a bone is that which it owes to 

 the relations existing between its three dimensions length, width, and 

 thickness, a. A bone in which one of its dimensions much exceeds those of 

 the other two is a long bone. Example : the femur. All the long bones are 

 hollowed out internally by an elongated space the medullary cavity. Long 

 bones belong exclusively to the limbs. In the animal economy, there are found 

 bones which resemble them in their dimensions, but they have no medullary 

 canal. Example : the ribs. These differ essentially from the true long 

 bones, and are sometimes distinguished from them by the appellation of 

 elongated bones, b. A bone that offers two dimensions much more developed 

 than the third, is a flat or wide bone. Example : the parietal bone. The 

 bones of this category, destitute of a medullary cavity, are met with in the 

 head and the upper regions of the limbs, 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 cavity, 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 

 form. 



EXTERNAL PECULIARITIES OP BONES. These markedly attract the atten- 

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

 us in distinguishing one bone from another. These peculiarities, which are 

 real distinctive features that permit their description to be precisely esta- 

 blished, are always either eminences (processes) or depressions. 



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 

 synarihrodial eminences, according as they belong to movable or immovable 

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

 and muscles, are called non-articular, or eminences of insertion. 



(The term imprint 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 im- 

 prints, according as they give attachment to muscles, tendons, ligaments, or 

 aponeuroses.) 



The synarfhrodial eminences are always indentations more or less deep 

 and finely cut. 



