318 NERVOUS SYSTEM. 



the brachial plexus in mammalia, and of the lumbar plexus in 

 the frog.* 



Ganglions are knots which occur in the course of nerves, 

 whereby they have, for the time, a great augmentation of vo- 

 lume. The ganglions have a great variety of form and size ; 

 they are parabolic, circular, crescentic and so on; and, in their 

 general appearance, hardness, and colour, resemble somewhat 

 lymphatic glands. Their structure Is intricate, and as yet ra- 

 ther unsettled. When submitted to maceration, they are re- 

 solved into two kinds of substance; one is filamentous and con- 

 tinuous with the nerves, adhering to the ganglion; and the other 

 is gelatinous and of a reddish ash colour. The filaments, in 

 penetrating the ganglions are deprived of their neurileme, which 

 is continued into a sort of capsule that surrounds the ganglions. 

 They pass uninterruptedly through the ganglion, and, therefore, 

 continue the several nervous cords into one another; but, in a 

 complicated way. The nature of the gelatinous substance is not 

 fully ascertained ; by some, and Scarpa among others, it is 

 thought to be fat. The ganglions, like other parts of the nervous 

 system, are very vascular. 



The Ganglions are said to be simple and compound; the first 

 is where a single nerve produces the ganglion, and the second 

 where the filaments of two or more nerves concur to form it. 

 The simple ganglions are invariable in their form and situa- 

 tion, and belong to the spinal marrow, being formed upon the 

 posterior fasciculi alone: this fact was first pointed out by 

 Haase,| and has been subsequently confirmed by the observa- 

 tions of Scarpa and of Prochaska, and by the admission of 

 anatomists generally. The exterior envelope is continuous 

 with the dura mater, arid the internal with the pia mater, from 

 whence they have more firmness than other ganglions. The 

 compound ganglions are found at divers stations about the 

 body. 



The attention of the profession has been much directed lat- 

 terly to the microscopical observations of Professor Ehrenberg, 



* Mailer's Report on Nervous System, p. 232, for the year 1836. 

 | De Gangliis Nervcrutn. Leipsick, 1772. 



