ELASTIC OR YELLOW CARTILAGE. Ixxxv 



Development of hyaline cartilage. The parts of the embryo which are about to 

 become cartilages are made up at first of the common embryonic cells from which the 

 tissues generally originate. The cell-contents clear up, the nucleus becomes more 

 visible, and the cells, mostly of polygonal outline, appear surrounded by clear lines of 

 pellucid substance, forming as it were a network of bright meshes inclosing them, 

 but in reality consisting of the cohering capsules of the contiguous cells, and consti- 

 tuting all that exists of the matrix at this time. Amyloid matter appears at an 

 early period in the protoplasm of cartilage-cells. Rouget found it in the sheep's 

 embryo of two months, both in ossifying cartilage and in the cartilages of the 

 trachea. The subsequent changes consist in enlargement and multiplication of the 

 cells and development of the intermediate matrix. The cells multiply by division. 

 The process is described at page xvii, although all the successive steps there 

 described and represented in the figure (xn.) have not been actually traced. In 

 growing cartilage from the frog-larva, Heidenhain* observed a double (i.e. divided) 

 nucleus in some cells, and in certain of these a straight linear partition running 

 across the cell between the two nuclei. This partition was recognised to be double, 

 and doubtless formed by the contiguous thin capsules of two new cells formed by 

 division of the previously single one. It is doubtful how the capsule or secondary 

 cell-wall is produced ; whether excreted by the cell which it afterwards incloses, as 

 held by Kb'lliker, or formed by conversion of a superficial layer of the protoplasm of 

 the cell-body, as taught by Max Schultze, or a primarily independent deposit round 

 the cells. However this may be, there is at first no matrix but what is made up of 

 the simple capsules. In further growth there is a difference, according as the cells do 

 or do not undergo frequent division. In the latter case a cell becomes surrounded 

 by many concentric capsules formed in succession ; that is, the first capsule is ex- 

 panded, and the others formed each within its expanding predecessor, so that the 

 cartilage comes to consist of scattered cells, each with a concentric system of capsules, 

 which by means of re-agents may be rendered visible in the neighbourhood of the 

 cells, but further off are inseparably blended into an uniform substance. When, on the 

 other hand, the cells have a tendency to frequent subdivision, the new capsules are 

 produced by the new cells, and are included in and finally blend with those which 

 had belonged to the previous cells, as shown by fig. xn. 



The matrix, although thus formed of the capsules, becomes to all appearance homo- 

 geneous ; but in sections of cartilage that have been exposed to acids and other re- 

 agents, the contour lines of the capsules round cells and cell-groups may be more 

 or less distinctly brought into view. But, whilst admitting that the capsules have a 

 share in the production of the matrix, Kb'lliker and some other histologists incline 

 to the opinion that part of it is an independent deposit. Heidenhain, however, has 

 found that, when thin sections of cartilage are digested for twenty-four hours in water, 

 at from 112 to 122 F., or in diluted nitric acid with chlorate of potash for a greater 

 or less time according to the degree of dilution, the matrix becomes parted or 

 marked off into polygonal areas corresponding to the larger groups of cells, and these 

 again into smaller groups, or single cells, without any intervening substance ; the 

 whole matrix thus appearing to be portioned out into segments, each appertaining to 

 a larger or smaller group of cells, and in all probability representing the aggregated 

 capsules belonging to them. 



The vital changes which occur in cartilage take place very slowly. Its mode of 

 nutrition has been already referred to ; it is subject to absorption, and when a 

 portion is absorbed in disease or removed by the knife, it is not regenerated. Also, 

 when fractured, as sometimes happens with the rib-cartilages, there is no reunion by 

 cartilaginous matter, but the broken surfaces become connected, especially at their 

 circumference, by fibrous or dense areolar tissue, often by a bony clasp. But, not- 

 withstanding that normally it is not regenerated, hyaline cartilage occurs in perfectly 

 characteristic form as a morbid product in certain tumours. 



ELASTIC OR YELLOW CARTILAGE. 



The epiglottis and cornicula of the larynx, the cartilages of the ear and of 

 the Eustachian tube, differ so much from the foregoing, both in intimate 



* Studien des Physiologischen Instituts zu Breslau, 2ter Heft, 1863. 



