374 



THE MICROSCOPE. 



be strictly termed intercellular. The cells are frequently or entirely 

 isolated, as seen in the section from the ear of a mouse (Fig. 176, 

 No. 1) ; and it then rarely becomes converted into bone. In the 

 higher animals it is generally invested by a fine and delicate mem- 

 brane, termed perichondrium, which brings blood-vessels into close 



fig. 177. 



1. Cartilage from the cuttle-fish, showing a peculiar form of cell. 2. Cartilage from 

 the head of skate, with nucleated cells in clusters, and nucleoli in their interior. 

 3. Cartilage from the frog, and cells having nucleoli : magnified 200 diameters. 



contact with the cartilage ; and when in actual contact with the ex- 

 tremities of bones, it is covered by a fringed membrane having a large 

 number of vessels terminating in it, for the purpose of supplying a 

 lubricating fluid to the end of the bones : this is the synovial mem- 

 brane, a very beautiful structure when injected and viewed with the 

 1 or 2 inch object-glass. 



In the early stages of existence, the framework, or a very large 

 proportion of it, is composed of cartilage, which, by the gradual addi- 

 tion of earthy matter, becomes consolidated into bone. The mode of 

 development, and the change from one to the other, is represented in 

 the section, Plate XII. No. 8 ; it will there be seen that the calcareous 

 matter is deposited in nearly straight lines, which stretch from the 

 ossified surface into the substance of the matrix of the cartilage, the 

 amount of calcareous matter in which gradually diminishes as we 

 recede from the ossified part. If the deposit has taken place to any 

 great extent, the calcareous matter becomes crowded and consolidated ; 

 as the process advances, the bone thickens, and a series of grooves, of 

 a stellate figure, No. 9, are found upon its surface, which are gradually 

 converted into canals for the passage of blood-vessels. 



