THE NERVOUS TISSUES. 



77 



FIG. 93. 



junction of several fibres being frequently marked by characteristic 

 triangular areas, in which a number of the nerve-nuclei are often 

 collected. 



THE NERVE-TRUNKS. 



The nerve-fibres already described are associated in bundles the 

 funiculi which, in turn, may be grouped to constitute the large 

 macroscopic nerve-trunks. The 

 funiculi differ greatly in diameter, a 

 number of varying size being usually 

 included within the nervous cord; 

 in very small nerves, however, a 

 single funiculus may suffice to form 

 the entire trunk. While both kinds 

 of fibres are grouped in bundles, 

 the nerves composed principally of 

 medullated fibres present the more 

 typical arrangement. 



On transverse section of such 

 trunks the individual nerve-fibres 

 appear as small, round, nucleated 

 cells, whose somewhat eccentrically 

 placed nuclei are the axis-cylinders 

 in section, while the contours of the 

 cell-like areas are formed by the 

 sections of the neurilemma ; the 

 shrunken granular or concentrically 

 marked masses within the apparent 

 cell-walls are the remains of the 

 medullary substance. These sec- 

 tions of the fibres are held in place 

 by a delicate connective tissue 

 among and surrounding the individual fibres. When the nerve- 

 bundle, or funiculus, is small, the nerve-fibres are uniformly dis- 

 tributed, and it is spoken of as simple ; when large, however, the 

 fibres are usually divided into irregular groups by stronger fibrous 

 trabeculae, thus forming a compound funiculus. The individual 

 nerve-fibres vary greatly in diameter (from 2 to 20 /*), even adjoining 

 fibres often exhibiting marked differences. In general, the cerebro- 

 spinal nerves possess the largest fibres, the sympathetic much the 

 smallest (2 to 4 //), while the components of many of the cranial 

 nerves occupy an intermediate position. 



Each funiculus is invested by a robust connective-tissue sheath 

 the perineurium between the fibrous lamellae of which are seen 



Section of portion of a nerve-trunk including 

 three bundles, or funiculi, surrounded by the ,-/' c. 

 perineurium (/); the funiculi, together with 

 the blood-vessels and adipose tissue, are 

 united by the more general epineurium (e) ; 

 the sections of the individual nerve-fibres are 

 held in place by the endoneurium ; f t fat-cells, 

 near which are the sections of blood-vessels. 



-the endoneurium extending 





