THE NERVOUS TISSUE. 



1125 



on approaching the muscular fibre, suddenly loses its white matter of Schwann, 

 which abruptly terminates ; the neurilemma becomes continuous with the sarco- 

 lemma of the muscle, and only the axis-cylinder enters the muscular fibre, where 

 it immediately spreads out, ramifying like the roots of a tree, immediately beneath 

 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. 



The Ganglia may be regarded as separate small aggregations of nerve-cells, 

 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 sensory root of the fifth cranial nerve ; on the facial 

 and auditory nerves ; and on the glosso-pharyngeal 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 brandies of the cerebro-spinal sys- 

 tem. 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 perineurium of the nerves, and sends 

 numerous processes into the interior of 

 the ganglion, which support the blood- 

 vessels supplying its substance. 



In structure all ganglia are essen- 

 tially similar (Fig. 664), consisting of 

 the same structural elements as the other 

 nervous centres, viz., a collection of 

 nerve-cells and nerve-fibres. Each nerve-cell has a nucleated sheath, which is 

 continuous with the sheath of the nerve-fibre with which the cell is connected. 

 The nerve-cells in the ganglia of the spinal nerves are pyriform in shape, and 

 have only one process, the axis-cylinder or axon. A short distance from the cell, 

 and while still within the ganglion, this process divides in a T-shaped manner, one 

 limb of the* cross-bar passing centrally and forming the central portion of a sen- 

 sory nerve-fibre ; the other limb passing peripherally to form the axis-cylinder 

 process of the peripheral nerve-fibre. In the sympathetic ganglia the nerve-cells 

 are multipolar and have one axis-cylinder process or axon and several protoplasmic 

 processes or dendrons. The former of these emerges from the ganglion as a non- 

 medullated nerve-fibre. Similar cells are found in the ganglia connected with the 

 fifth cranial nerve, and these ganglia are therefore regarded by some as the cranial 

 portions of the sympathetic system. The nerve-cells are disposed in the ganglia 

 in groups of varying size, and these groups are separated from each other by 

 bundles of nerve-fibres, some of which traverse the ganglia without being con- 

 nected with the cells. 



FIG. 664. Section through a microscopic ganglion. 

 Magnified 300 diameters. (Klein and Noble 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. 



