260 



Or THE PRIMARY TISSUES OF THE HUMAN BODY. 



Fig. 51. 



Section of the branchial Cartilage of Tadpole : a, 

 group of four cells, separating from each other ; b, pair 

 of cells in apposition ; c, c, nuclei of cartilage cells ; d, 

 cavity containing three cells. 



groups, in the Articular cartilages, which may be considered as the types of the 

 purely cellular form, usually lie perpendicularly in the deeper part of the car- 

 tilage (that nearest the attached sur- 

 face), and obliquely or irregularly as 

 they approach the free surface, whilst 

 at and near that surface they lie pa- 

 rallel to it. The deeper groups are 

 composed of a larger number of cells 

 than the superficial ; and in the stra- 

 tum forming the free surface, single 

 isolated cells are not unfrequent, 

 which have been mistaken for epi- 

 thelium-cells. The free surface is 

 covered in the fcetal state by a syno- 

 vial membrane; of which the two 

 characteristic elements basement 

 membrane and epithelial cells may 

 be clearly recognized. But after 

 birth, this membrane seems to be 

 gradually destroyed by pressure and 

 attrition, and by the retirement of 

 the superficial vessels towards the circumference ; and appears in the adult to 

 terminate at the margin of the cartilage, very little in advance of the " circulus 

 articuli vasculosus." The matrix of the cartilage-cells is not as perfectly homo- 

 geneous as its appearance in thin sections would seem to indicate ; for when a 

 shred of it is detached from the edge of a fractured cartilage, it is found to 

 tear in a distinctly filamentous manner ; and the arrangement of the filaments 

 corresponds with that of the cells, being perpendicular to the attached surface 

 of the cartilage, and parallel to its free surface, where it forms with the cells a 

 sort of membranous layer that has been mistaken for synovial membrane. 1 It 

 is interesting to observe that this filamentous arrangement of the intercellular 

 substance becomes much more obvious in certain diseased states of articular 

 Cartilages ; and that, concurrently with this change, its chemical composition 

 alters from chondrin to gelatin. 3 



252. The varieties in the permanent Cartilages principally depend upon the 

 degree of organization which subsequently takes place in the intercellular sub- 

 stance. If a mass of Fibres, analogous to those of the fibrous membranes 

 ( 220), should originate in it, the Cartilage presents a more or less fibrous 

 aspect (Fig. 52) ; in some instances the Fibrous structure is developed so much at 

 the expense of the cells, that the latter disappear altogether, and the whole 

 structure becomes fibrous. Sometimes the fibres which are developed are 

 rather analogous to those of the Elastic tissue ( 221); these are disposed 

 around the cells, forming a kind of network, in the areolse of which they lie ; 

 and this kind of cartilage may be termed the elastic or reticular. The primi- 

 tive cellular organization is for the most part retained in the ordinary articular 

 cartilages, 3 the cartilaginous septum narium, the cartilages of the alae and point 



1 See the excellent account of the structure of Cartilage by Prof. Sharpey, in his Intro- 

 duction to " Quain's Elements of Anatomy," vol. i. p. 239, Am. Ed. ; and Dr. Leidy's Memoir 

 " On the Intimate Structure and History of Articular Cartilages," in the "Amer. Journ. 

 of Med. Sci.," April, 1849. 



2 This was first pointed out by Dr. Redfern, in his admirable Treatise on "Anormal 

 Nutrition in the Human Articular Cartilages." 



3 The articular cartilages, at the points where tendons are implanted into them, have 

 all the characters of fibro-cartilage ; the fibres of the tendon being spread through the in- 

 tercellular substance of the cartilage, for some distance, and gradually coalescing with it. 



