746 



DISTRIBUTION OF CAPILLARIES. 



network with rounded meshes, so as to distribute the blood among 

 the Fat-cells (§ 564) ; whilst in Fig. 396 we see the meshes enor- 

 mously elongated, so as to permit the Muscular Fibres (§ 567) to lie 

 in them. Again, in Fig. 397 we observe the disposition of the 



Fig. 397. 



Fig. 398. 



Distribution of Capillaries 

 in Mucous Membrane. 



Distribution of Capillaries 

 in Skin of Finger. 



Capillaries around the orifices of the Follicles of a Mucous mem- 

 brane ; whilst in Fig. 398 we see the looped arrangement which 

 exists in the Papillary surface of the Skin, and which is subser- 

 vient to the nutrition of the Epidermis and to the activity of the 

 Sensory Nerves (§ 572). 



583. In no part of the Circulating apparatus, however, does 

 the disposition of the Capillaries present more points of interest 

 than it does in the Respiratory organs. In Fishes the respiratory 

 surface is formed by an outward extension into fringes of Gills, 

 each of which consists of an arch with straight laminae hanging 

 down from it ; and every one of these laminae (Fig. 399) is fur- 

 nished with a double row of leaflets, which is most minutely sup- 

 plied with blood-vessels, their network (as seen at a) being so close 

 that its meshes (indicated by the dots in the figure) cover less space 

 than the vessels themselves. The Gills of Fish are not ciliated on 

 their surface, like those of Mollusks and of the larva of the Water- 

 Newt ; the necessity for such a mode of renewing the fluid in 

 contact with them being superseded by the Muscular apparatus 

 with which their gill -chamber is furnished. — But in Reptiles the 

 Respiratory surface is formed by the walls of an internal cavity, 

 that of the Lungs: these organs, however, are constructed on a 

 plan very different from that which they present in higher Verte- 

 brata, the great extension of surface which is effected in the latter 

 by the minute subdivision of the cavity not being here necessary. 

 In the Frog (for example) the cavity of each lung is undivided ; its 

 walls, which are thin and membranous at the lower part, there 

 present a simple smooth expanse ; and it is only at the upper part, 

 where the extensions of the Tracheal cartilage form a network over 



