8o NORMAL HISTOLOGY. 



it is thin enough to be examined with tolerably high 

 powers. It is stained double and mounted in balsam. 



The irregular chambers, lined with osteoblast and 

 filled with blood-vessels and marrow, which are formed 

 in the bones of the skull-cap at a later period, are well 

 shown by transverse sections through the decalcified 

 skull-bones of an older foetus (human, at about six or 

 seven months, or from the beef or sheep, sixteen to 

 twenty cms. long). These should be stained and mounted 

 as above. 



TEETH. 



The teeth have many structural features in com- 

 mon with bone. The chief bulk of the tooth is 

 made up of homogeneous, brittle basement sub- 

 stance, much harder than bone, called dentine. The 

 dentine contains lime salts, and is permeated by a 

 multitude of fine branching channels which radiate 

 from a central cavity, called the pulp cavity, which 

 the dentine encloses. These delicate channels in 

 the dentine are analogous with the canaliculi of 

 bone. 



The pulp cavity is filled with a soft vascular 

 tissue, called /&//>, containing irregular-shaped, often 

 branching cells and nerves. Along the sides of the 

 pulp cavity lie spheroidal or ovoid cells, which send 

 off branches into the pulp and also into the above- 

 mentioned delicate channels in the dentine. These 

 cells are called odontoblasts or dentine cells, and are 

 usually considered to be analogues of the bone- 



