THE SKELETON 1 9 



one, and the metacarpals, metatarsals, arid phalanges two 

 centers of ossification in man. This probably holds for the 

 rabbit also. By far most of the bones are formed by the process 

 of replacement. 



Bones are classified according to their form, as a means of 

 ready reference. Although this method of classification 

 suggests the function, it is limited in application to the bones 

 themselves. Thus, in reference to the shape of the bones, the 

 four classes are: (i) Long bones, those having a diaphysis 

 (shaft) , which is usually filled with yellow marrow, and typically 

 two epiphyses (separately ossified ends) which ultimately 

 fuse with the extremities of the diaphyses. Some noteworthy 

 exceptions are found in the metacarpals, metatarsals, and 

 phalanges which have only one epiphysis. Examples of 

 typical long bones are the clavicle, humerus, radius, ulna, 

 metacarpals, phalanges, and femur. (2) Short bones have 

 little cancellous tissue and no cavity, e.g., carpals and tarsals. 

 (3) Flat bones have a layer of cancellous tissue between the 

 two other layers of very compact tissue, e.g., innominate bone, 

 scapula, and parietals. (4) Irregular bones are of various 

 forms and structure, e.g., vertebrae, temporals, mandible, and 

 practically all others which do not fit into the preceding groups 

 readily. 



C. RELATIONS AND TOPOGRAPHY OF SOME OF 

 THE BONES 



a. THE SKULL 



The skull of the rabbit (Figs. 2, 3) does not usually lend 

 itself to intensive study due to the fact that in laboratory 

 material it is seldom well ossified. However, the general form 

 and relations of the principal bones may be seen readily. 



The occipital bone forms the base of the skull; furnishes 

 two processes, occipital condyles, for the articulation of the 

 atlas; articulates with the sphenoid ventrally and with the 

 interparietal cranially; and surrounds the foramen magnum. 



