40 HUMAN PHYSIOLOGY. 



According to the amount and texture of the ground substance, three 

 principal varieties may be distinguished : 



1. Hyaline cartilage, in which the cells, relatively few in number, are 

 embedded in an abundant quantity of ground substance. The body 

 of the cells is in many instances distinctly marked off from the 

 surrounding substance by concentric lines or fibers, which form a 

 capsule for the cell. Repeated division of the cell substance takes 

 place, until the whole capsule is completely occupied by daughter 

 cells. The ground substance is pervaded by minute channels, 

 which communicate on one hand with the spaces around the cells, 

 and on the other with lymph-spaces in the connective tissue sur- 

 rounding the cartilage. By means of these channels, nutritive 

 fluid can permeate the entire structure. Hyaline cartilage is 

 found on the ends of the long bones, where it enters into the for- 

 mation of the joints; between the ribs and sternum, forming the 

 costal cartilage, as well as in the nose and larynx. 



2. White fibre-cartilage, the ground substance of which is pervaded 

 by white 'fibers, arranged in bundles or layers, between which are 

 scattered the usual encapsulated cells. White fibro-cartilage is 

 tough, resistant, but flexible, and is found in joints where strength 

 and fixedness are required. Hence it is present between the ver- 

 tebrae, forming the intervertebral discs, between the condyle of the 

 lower jaw and the glenoid fossa, in the knee-joint, around the 

 margins of the joint cavities, etc. In these situations it assists in 

 maintaining the apposition of the bones, in giving a certain degree 

 of mobility to the joints, and in diminishing the effects of shock 

 and pressure imparted to the bones. 



3. Yellow fibro-cartilage, the ground substance of which is pervaded 

 by opaque, yellow elastic fibers, which form, by the interlacing of 

 their branches, a complicated network, in the meshes of which are 

 to be found the usual corpuscles. As these fibers are elastic, they 

 impart to the cartilage a very considerable degree of elasticity. 

 Yellow fibro-cartilage is well adapted, therefore, for entering into 

 the formation of the external ear, epiglottis, Eustachian tube, etc. 

 structures which require for their functional activity a certain 

 degree of flexibility and elasticity. 



Osseous Tissue. Osseous tissue, as distinguished from bone, is a 

 member of the connective-tissue group, the ground substance of 

 which is permeated with insoluble lime salts, of which the phos- 



