286 



ANIMAL PHYSIOLOGY. 



[LESSON 88. 



1282. In a portion of human pericardium (the bag in which the 

 heart hangs) very minutely injected, and presenting a most gorgeous 

 sight under the microscope, three somethings are seen entering the 

 tissue at a particular point, somewhat deep seated, and to some extent 

 veiled by a plexus of capillaries belonging to that layer of tissue which 

 covers them ; what are they ? Many circumstances lead to the con- 

 clusion that the outer vessel on one side (6, Fig. 408) is an artery, 

 distributing blood to the pericardium, and that the outer vessel, on 

 the opposite side (a), is the vein, receiving and returning the blood 

 from this tissue ; but what is the third something which lies between 

 them ? Let us examine it closely, and see if we can discover what 

 it is ; two vessels make their appearance, one on either side of this 

 something the one is much smaller than the other, and both appear 

 to be connected with the capillary plexus (c) ramifying between them ; 

 no connection whatever appears to subsist between the outer vessels 



FIG. 409. 



FIG. 409. 



Portion of human pericardium. 



Vascularity of a ganglion, with the vessels of 

 supply and return. 



of the unknown tissue and the artery and vein outside of it ; the 

 question hence arises, in what tissue is such a distribution a peculiari- 

 ty? To this there can be but one reply a nerve and this some- 

 thing which, in the dried state of the tissue, more nearly resembles 

 another blood-vessel, is indeed the nerve which invariably accom- 

 panies the artery throughout its distribution. 



1283. If the circulation of the blood to a nerve be peculiar, it is 

 no less so to the ganglions ; for an example, a copy is given (Fig. 

 409) of a preparation of a sympathetic ganglion of the neck 

 (human). 



1284. Here the artery and vein are not at all connected with the 

 tissue to be supplied, but the former, while passing in its course of 

 general distribution, gives off a twig (a) to the ganglion, which in- 

 stantly breaks up into a plexus of capillaries, which ramify all over 



