LESSON 88.] NERVOUS SYSTEM IN MAMMALIA AND MAN. 



285 



(a), which, in the preparation, are slightly red, as they are in man. 

 All the figures of nerve tissue have been drawn under a one- 

 fourth object glass, and to scale. 



FIG. 407. 



LESSON LXXXYIII. 



NEEVOUS SYSTEM IN MAMMALIA AND MAN, CONCLUDED. 



1278. Vascularity of Nerves. Nerves, like muscles, appear to 

 be highly vascular ; the vessels, however, will be found restricted to 

 the outer sheath, and are not allowed to penetrate amongst the tubu- 

 lar structure. This rule also applies to the brain, which is nourished 

 and sustained, not by vessels passing into the interior of its substance, 



"but by a highly vascular membrane, the pia mater, which every- 

 where surrounds it. 



1279. Nerves, it is well known, always accompany the arteries 

 and veins into whatever tissue they are distributed, but the nerves 

 do not gain any advantage from their near proximity to arteries 

 during the course of their joint dis- 

 tribution, for the nerves carry their 



own vascular system with them. 



1280. In good injected prepara- 

 tions the nerves will be found to have 

 participated in the general success; 

 if one of these be dissected out, placed 

 on a slip of glass, dried, and mounted 

 in Canada Balsam, the probability is 

 that an appearance will present itself, 

 under the microscope, similar to Fig. 

 407, which shows an injected nerve. 

 On one side of the sheath will be seen 

 an artery (a), and on the opposite 

 side a vein (5), and these two vessels 



are connected by a series of capillaries (c), which ramify everywhere 

 on the surface of the sheath. 



1281. Such a preparation as the foregoing, is very instructive, as 

 it teaches a lesson not easily forgotten ; it demonstrates the peculiar- 

 ity of the distribution of vessels in this particular tissue, and enables 

 one to detect a nerve, under circumstances in which it would other- 

 wise elude detection. 



Nerve injected. 



