104 THE HUMAN BODY. 



membranes : the flat cells (Fig. 11, I) which form the 

 epithelium of the serous cavities are themselves a layer of 

 modified connective-tissue corpuscles. 



In brain and spinal cord, protecting and supporting the 

 nerve-tissues, are found branched cells forming the neuroglia. 

 They are not true connective tissue, but correspond to cells 

 of the horny layer of the epidermis, shut in when the 

 medullary canal was closed in the embryo. 



Elastic Cartilage and Fibro-cartilage. We may now 

 return to cartilages and consider those forms which are made 

 up of more or less true cartilage mixed with less or more con- 

 nective tissue of one kind or another. The cartilages of the 

 ear and nose and some others have their matrix pervaded by 

 fine branching fibres of yellow elastic tissue, which form net- 

 works around the groups of cartilage-cells. Such cartilages 

 are pliable and tough and possess also considerable extensibil- 

 ity and elasticity. They are known as elastic or, from their 

 color, as yellow cartilages. Elsewhere, especially in the carti- 

 lages which lie between the bones in some joints, we find 

 forms which have the matrix pervaded by white fibrous tissue 

 and known as fibro-cartilage. For example the articular 

 cartilage on the end of the lower jaw does not come into 



FIG. 48. Section through the joint of the lower jaw showing its interarticular 

 fibre-cartilage, x, with the sy no vial cavity on each side of it. 



direct contact with that covering its socket on the skull, but 

 lying between the two in the joint (Fig. 48) is an interartic- 

 ular fibro-cartilage : similar cartilages exist in the knee-joint; 



