550 ELEMENTARY PHYSIOLOGY 



177, c) for the cells ; and, at times, the matrix may by 

 appropriate methods be split up into pieces, each belonging 

 to and surrounding a cell, or group of cells, and often 

 disposed in concentric layers. 



Close to the perichondrial surface of the cartilage the 

 cells become smaller and separated by less intercellular 

 substance, until at length the transparent chondrigenous 

 material is replaced by the fibrous collagenous substance 

 of connective tissue (p. 554), and the cartilage cells take 

 on the form of "connective tissue corpuscles." 



In a very young embryo we find in the place of a 

 sterno-cnstal cartilage nothing but a mass of closely- 

 applied, undifferentiated, nucleated cells, having the same 

 essential characters as colourless blood-corpuscles, or as 

 the deepest epidermic cells. The rudiment, or embryonic 

 model of the future cartilage thus constituted, increases 

 in size by the growth and division of the cells. But, 

 after a time, the characteristic intercellular substance 

 appears, at first in small quantity, between the central 

 cells of the mass, and a delicate sterno-costal cartilage is 

 thus formed. This is converted into the full-grown 

 cartilage (a) by the continual division and subsequent 

 growth to full size, of all its cells, and especially of those 

 which lie at the surface ; (6) by the constant increase in 

 the quantity of intercellular substance, especially in the 

 case of the deeper part of the cartilage. 



The manner in which this intercellular substance is 

 increased is not certainly made out. If the outermost 

 layer only of each of the protoplasmic bodies of adjacent 

 cells of the epidermis were to become cornified and fused 

 together into one mass, while the remainder of each 

 cell continued to grow and divide and its progeny threw 

 oflf fresh outer cornified layers, we should have an epi- 

 dermic structure which would resemble cartilage except 

 that the "intercellular substance" would be corneous 

 and not chondrigenous. And it is possible that the 

 intercellular aubstance of cartilage may be formed in this 



