Ixxx CARTILAGE. 



DEVELOPMENT OF CONNECTIVE TISSUE. 



In those parts of the embryo where connective tissue is to be developed, there is at 

 first a deposit of nucleated corpuscles, having the characters common to the cells of 

 which the early embryo-body throughout consists. Between the cells is a small 

 amount of soft amorphous intercellular substance, which increases in quantity. This 

 is at first of a muco-albuminous nature, but is in great part changed into a gela- 

 tinous substance, which assumes a fibrillar character, and becomes converted into the 

 bundles of white wavy filaments that constitute the chief part of the areolar and 

 fibrous tissues. These bundles, after their first appearance, increase in size, and con- 

 tinue to grow larger after birth. Amongst these white fasciculi, elastic fibres, in 

 varying proportion, appear at a somewhat later period. These are also produced 

 from the intercellular substance, which in this case undergoes a different chemical 

 change. They appear from the first in form of networks pervading the intercellular 

 mass throughout, and not as single shorter fibres gradually lengthening out and joining 

 together ; nor do they appear to be formed by the linear coalescence of granules, but by 

 immediate differentiation in the intercellular substance. The elastic fibres are at 

 first exceedingly fine, but acquire greater thickness as development advances, and in 

 some situations what was originally a network may become an elastic membrane. 

 The cells in part remain as the connective-tissue-corpuscles already described; irre- 

 gularly ramified in open areolar tissue, but fusiform within the bundles and in the 

 interstices of dense fibrous tissue ; part of them become filled with fat, and form the 

 adipose tissue. The intercellular substance is usually reduced to an inconspicuous 

 amount, but in some situations remains in notable quantity. 



Such is the most general course of development ; but, as will be understood from 

 what has preceded, it is different in particular cases. Thus, the intercellular sub- 

 stance may accumulate in large proportion, and the cells finally disappear, as in the 

 vitreous humour ; or the cells may be developed into retiform or cytogenous tissue, 

 without the formation of fibres, either white or elastic, in which case the jelly like 

 substance may remain, as in the enamel-organ; or the reticular interstices may become 

 filled with the elements of another tissue, as in the lymphatic glands and nervous 

 centres. In the development of the pure elastic ligaments the cells shrink as the 

 elastic fibres grow larger, and at length disappear altogether. 



The intercellular substance may be excreted by the cells, but there is no clear 

 proof of this ; it may be an independent deposit between them ; and the disappearance 

 of the cells from pure elastic ligament would seem to show that, whatever be the 

 influence they exert in the original formation, they are not needed for carrying on 

 the nutrition, or even for the further growth of the tissue. 



The foregoing account of the formation of connective tissue is derived from Kb'l- 

 liker's latest observations;* but Max Schultze considers that the intercellular sub- 

 stance, or matrix, is neither excreted by the cells, nor deposited ab extra, but is in 

 reality formed by conversion of part of the protoplasm which forms the bodies of the 

 cells (nucleated protoplasm-masses) : the matrix thus increases and becomes fibrillated 

 at the expense of the cells, which, now reduced to the nuclei surrounded with a small 

 portion of protoplasm, remain as the connective-tissue-corpuscles. 



CARTILAGE. 



This is the well-knowu substance commonly called " gristle." The follow- 

 ing are its more obvious characters. When in mass, it is opaque and of a 

 pearly or bluish white colour, in some varieties yellow ; but in thin slices ifc 

 is translucent. Although it can be easily cut with a sharp knife, it is 

 nevertheless of very firm consistence, but at the same time highly elastic, 

 so that it readily yields to pressure or torsion, and immediately recovers its 

 original shape when the constraining force is withdrawn. By reason of 



* Neue Untersuchungen iiber die Entwickekmg des Bindegewebes. Wiirzb. naturwiss. 

 Zeitschr., vol. ii. Also Handbuch der Gewebelehre, 4th edit. 1863. 



