DISTRIBUTION OF THE CAPILLARIES. 333 



capillaries has an evident reference to these (Fig. 97) ; whilst, on the 

 other hand, where the surface of the skin is raised up into sensory 

 papillae, the capillary network sends looped prolongations into them, 

 which are found accompanying their nerves (Figs. 98 and 99). 



591. It cannot be supposed that the arrangement of the vessels has 

 any further influence upon the function of the part they traverse, than 



Fig. 97. Fig. 98. 



Distribution of Capillaries around follicles Distribution of Capillaries at the surface of 



of Mucous Membrane. the skin of the finger. 



that which it derives frorn the regulation of the supply of blood afforded 

 to each individual portion of the structure. The form of the capillary 



Fig. 99. 



Capillary Network of fungifonn papilla of the tongue. 



network is evidently determined by that of the elements of the tissues 

 permeated by it ; these are the real operative instruments in every part ; 

 and the distribution of the blood-vessels is so arranged, as to afford 

 them precisely the amount of nourishment they respectively require. 

 Thus -we have seen, that there are many living parts, possessing most 

 important functions, in the human body, which are not in any direct 

 relation with blood-vessels, and which yet derive their whole nutriment, 

 and the materials of their functional operations-, from the blood. This 

 is the case, for example, with the whole of the epithelial and epidermic 

 cells ; and also with the articular cartilages, and the substance of the. 

 teeth. Even in bone, the islets between the Haversian canals, which 

 are completely unpenetrated by vessels, are of considerable size. Such 

 islets must everywhere exist, between the meshes of the capillary net- 

 work ; so that the question of the vascularity or non-vascularity of a 

 tissue is one of degree only ; the ultimate fibre of muscle or nerve, 

 and the cells and fibres of other tissues, being as completely non- vascular, 

 as the entire substance of a tooth or of an articular cartilage ; the latter 

 being nourished, like the former, by imbibition from the surrounding 

 vessels. 



592. The term "Capillary" may be employed in an extended or a 



