io2 COMPARATIVE ANATOMY 



head of a bone or from the hyoid, sternum, or supra-scapula of 

 a frog be examined under the microscope, it is seen to consist 

 of nucleated cells imbedded in a matrix of firm gelatinous 

 consistency, which can easily be cut with a knife, but is at the 

 same time highly elastic ; it may be bent, twisted, or com- 

 pressed, but readily recovers its size and shape when freed 

 from the stress to which it was subjected. Like the inter- 

 cellular substance of connective tissue the matrix of cartilage 

 is readily stained by nitrate of silver. 



Fig. 20. 



Part of a section through the xiphisternum of a frog to show the structure of 

 hyaline cartilage. Several cartilage cells, many of them in groups of 

 two, are imbedded in a hyaline matrix. 



There are several kinds of cartilage, hyaline, calcified, and 

 fibrous cartilage ; the last-named may be yellow or white, 

 according as the fibres in it are elastic or simply white fibres. 

 We will concern ourselves chiefly with hyaline cartilage, so- 

 called because of its homogeneous translucent matrix. The 

 cells imbedded in it are rarely disposed singly and at equal 

 distances from one another, but usually in groups or lines of 

 two, four, or more, and it is often noticeable that in a group 

 of two the cells are separated by a very small amount of inter- 

 vening matrix, and that their adjacent sides are flattened as 

 if by mutual pressure. Each cartilage cell is a subspherical 

 or lenticular corpuscle of protoplasm, containing a rounded 

 nucleus with a well-defined chromatin network, and a cell- 

 body, in which fine granules and interlacing fibrils may often 



