XER VO US TISSUE. 



79 



the sarcolemma. and is imbedded in a layer of granular matter, containing a 

 number of clear, oblong nuclei, the whole constituting an end-plate from which 

 the contractile wave of the muscular fibre is said to start. 



FIG. 55. Muscular fibres of Lacerta viridis with the terminations of nerves, a. Seen in profile. P.P. The nerve 

 end-plates, s.s. The base of the plate, consisting of a granular mass with nuclei, b. The same as seen in look- 

 ing at a perfectly fresh fibre, the nervous ends being probably still excitable. (The forms of the variously- 

 divided plate can hardly be represented in a woodcut by sufficiently delicate and pale contours to reproduce 

 correctly what is seen i'n nature.) c. The same as seen" two hours after death from poisoning by curare. 



The Ganglia may be regarded as separate and independent nervous centres, of 

 smaller size and les< complex structure than the brain, connected with each other, 

 with the cerebro-spinal axis, and with the nerves in various situations. They are 

 found on the posterior root of each of the spinal nerves ; on the posterior or sen- 

 sory root of the fifth cranial nerve; on the facial and auditory nerves: and 

 on the glosso-pharvngeal and pneumogastric nerves. They are also found in 

 a connected series along each side of 

 the vertebral column, forming the trunk 

 of the sympathetic: and on the branches 

 of that nerve, generally in the plexuses 

 or at the point of junction of two or 

 more nerves with each other or with 

 branches of the cerebro-spinal system. 

 On section they are seen to consist of 

 a reddish-gray substance, traversed by 

 numerous white nerve-fibres ; they vary 

 considerably in form and size; the 

 largest are found in the cavity of the 

 abdomen : the smallest, not visible to 

 the naked eye. exist in considerable 

 numbers upon the nerves distributed 

 to the different viscera. The ganglia 

 are invested by a smooth and firm. 

 closely-adhering, membranous envelope, 

 consisting of dense areolar tissue ; this 

 sheath is continuous with the peri- 

 neurium of the nerves, and sends nu- 

 merous processes into the interior of 

 the ganglion, which support the blood- 

 em supplying its substance. 



In structure all ganglia are essen- 

 tially similar (Fig. 56), consisting of the 

 same structural elements as the other 

 nervous centres viz. a collection of nerve-cells and nerve-fibres. The nerve- 

 or ganglion-cells in the ganglia of the spinal nerves are pyriform in shape, the 



FIG. 56. Section through a microscopic ganglion. 

 Magnified 300 diameters. (Klein and >ioble Smith.) 

 c. Capsule of the ganglion, n. Nerve-fibres passing out 

 of the ganglion. The nerve-fibres which entered the 

 ganglion are not represented. The nerve-fibres are 

 ordinary medullated fibres, but the details of their 

 structure are not shown, owing to the low magnifying 

 power. The ganglion-cells are invested by special 

 capsules, lined by a few nuclei, which are here repre- 

 sented as if contained in the capsule. 



