704 



THE MICROSCOPE. 



be strictly termed iuter cellular. Cells are frequently or 

 entirely isolated, as in the section from the ear of a Mouse 

 (fig. 332), they then rarely become converted into bone. 

 In the highest animals it is generally invested by a fine 



1 Fig. 335. 2 



1, Cartilage from the head of Skate, with clusters of nucleated cells anr) 

 nucleoli inclosed. 2, Cartilago from the Frog, with cells having nucleoli, 

 magnified 200 diameters. 



and delicate membrane, termed perichondrium, which brings 

 the blood-vessels in close contact with the cartilage ; and, 

 when in actual contact with the extremities of bones, is 

 covered by a vascular 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, the synovial 

 membrane, is a very beautiful structure when injected and 

 viewed under a 1-inch power. 



In the earliest stages of existence, the entire framework — 

 or a very large proportion — is composed of cartilage, which, 

 by a gradual addition of earthy matter, becomes consoli- 

 dated into bone. The mode of development, and the 

 change from one to the other, is represented in the section 

 (fig. 336) ; 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 



