THE SKELETON ^^ 



The laciince, or spaces for the bone cells during life, are 

 arranged concentrically about the Haversian canals. The 

 canaliculi, or processes of the lacunar, communicate with one 

 another. At the extremities of the bones the place of the 

 medullary canal is taken up by cancellous tissue (Fig. 14, d), 

 the compact tissue being very thin. The flat bones have no 

 medullary canal, but the diploe or cancellous tissue lying 

 between the outer compact tissue has its spaces filled with a 

 red marrow of the same nature as that in the cancellous tissue 

 of the long bones, wherein the red blood-corpuscles are formed. 

 The large medullary cavity or canal is filled with yellow or 

 fatly marrow. 



THE BONES OF THE HEAD 



The Skull As a Whole. — The skull is the expanded cranial 

 portion of the axial skeleton. It encloses the brain and affords 

 protection and support for the organs of taste, smell, sight, 

 and hearing. In the adult state, it is a very complex struc- 

 ture. It differs from the rest of the skeleton in that, save for 

 the mandible and hyoidean apparatus, its several parts are so 

 tightly joined together by immovable joints {synarthrosis) that 

 it can be separated only with great difficulty. Some of the 

 bones are so completely fused together that the individual 

 parts can no longer be recognized. A skull in which the bones 

 have been separated is known as a disarticulated skull. A skull 

 may be disarticulated by filling it with dried beans and soaking 

 in water for some time. 



When the skull of a cat is examined with respect to its 

 morphological structure it appears to be formed of three, or 

 including the olfactory capsule, four rings or segments. Each 

 of these rings is made up of a series of bones which enclose the 

 space occupied by the central nervous system. Older anato- 

 mists believed that they saw in these relations evidence for a 

 theory that the skull was formed by the fusion of four modified 

 vertebrae, each corresponding to one of these rings. This 



