FORMATION OF THE TISSUES CARTILAGE. 477 



the fluid that is supplied to the base of the hair may find its way upwards ; 



and there seems reason to believe, from the well-known fact of sudden change 

 of colour in the Hair under the influence of strong mental emotions, that, even 

 in its healthy state, fluid secreted at the base may be conveyed to its point. 

 In regard to the Development of Hair, no very satisfactory account can yet be 

 given ; as there are great differences of opinion amongst Microscopists as to 

 the precise mode in which it is effected. The pulp unquestionably consists of 

 an aggregation of nucleated cells ; and these, near the base of the hair, undergo 

 a change of form, their extremities being much prolonged, whilst their diame- 

 ter diminishes. They now form connected series, which adhere to each other, 

 and constitute what are known as the roots of the hair. By a process of meta- 

 morphosis, which is not yet properly understood, the outer cells of the pulp 

 become converted into the fibrous structure of the cortical substance, whilst 

 the inner ones form the medullary. It would seem as if, in simple hairs, this 

 last does not acquire its full development ; for it presents no appearance of dis- 

 tinct cells, such as those which are seen in the spine of the Porcupine or 

 Hedgehog ; but looks like the compressed contents of a number of cells, which 

 have themselves disappeared. 



025. In several of the Cartilages, the Cellular structure is very obvious, 

 whilst in others it has undergone a transition to the Fibrous. In all, however, 

 the early stage of formation appears to be the same. The structure originates 

 in Cells, analogous to those of which the rest of the fabric is composed ; but 

 between these cells a larger quantity than usual of hyaline or intercellular 

 substance is deposited ; and the amount of this substance continues increasing 

 simultaneously with the bulk of the cells. The original cells are pushed far- 

 ther and farther from one another; but new cells arise between them, from 

 cytoblasts which are formed in the hyaline substance. The first cells frequently 

 produce two or more young cells from their nuclei ; and thus it is very common 

 to meet with groups of such cells, which are known under the name of carti- 

 lage-corpuscles. The varieties in the persistent Cartilages principally depend 

 upon the degree of organization which subsequently takes place in the inter- 

 cellular substance. If a mass of Fibres, analogous to those of the fibrous 

 membranes ( 639), should originate in it, the Cartilage presents a more or less 

 fibrous aspect ; 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 ( 639) ; 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. The Cartilages which 

 are destined to become Bone, differ in structure from all these, but have the 

 same origin ; and when partial ossific deposits take place in old age, it is almost 

 invariably in the Cellular cartilage that they occur. The cartilaginous septum 

 narium, the cartilages of the alse and point of the nose, the semilunar cartilage 

 of the eyelids, the cartilages of the larynx (with the exception of the epiglottis), 

 the cartilage of the trachea and its branches, the cartilages of the ribs (in Man), 

 and the ensiform cartilage of the sternum, retain for the most part their primi- 

 tive cellular organization. The fibrous structure is seen in all those Cartilages 

 which unite the bones by synchondrosis ; this is the case in the vertebral 

 column and pelvis, the cartilages of which are destitute of corpuscles, except 

 in and near their centres. In the lower Vertebrata, however, and in the early 

 condition of the higher, the fibrous structure is confined to the exterior, and 

 the whole interior is occupied by the ordinary cartilaginous corpuscles. The 

 reticular structure is best seen in the epiglottis and in the concha auris : in the 

 former of these, scarcely any trace of Cartilage-Corpuscles remains ; in the 



