568 



NERVOUS SYSTEM. 



medium-sized fibre with borders of single con- 

 tour, and four large fibres ; of the latter, two 

 have a double contour, and two contain granu- 

 lar matter. 



these small fibres, which seem in many instances to be simple prolongations, without 

 alteration, of the axis-cylinder of the medulluted fibres, it will be seen that they are 

 chiefly found in the peripheral terminations of the nerves and in the filaments of connec- 

 tion of the fibres with the cells. The study of 

 the fibres in these relations constitutes the most 

 important part, physiologically, of the anatomy 

 of the nerves and presents the greatest difficul- 

 ties in the way of direct observation ; and, for 

 these reasons, we shall treat of these questions sep- 

 arately, and defer, for the present, the full con- 

 sideration of the non-medullated fibres. 



Gelatinous Nerve-Fibres (Fibres of Remak). 

 These fibres are entirely diiferent in their anat- 

 omy from either of the varieties of fibres just 

 considered. They are found chiefly in the sym- 

 pathetic system and in that particular portion of 

 this system connected with involuntary move- 

 ments. For instance, these fibres are very abun- 

 dant in the gray filaments sent to parts provided 

 with non-striated muscular fibres and endowed 

 with undoubted motor properties ; but they are 



from the human subject; not f oun( l j n fo e wn i te filaments of the sympa- 

 magmfied 3oO diameters. (Kolliker.) 



Four small fibres, of which two are varicose, one thetic, which seem to be incapable of exciting 



movements. 



There is considerable difference of opinion 

 among physiologists with regard to the gelatinous 

 filaments. Some are disposed to regard them as elements of connective tissue, not 

 endowed with properties characteristic of nerves, while others consider that they are 

 nerve-fibres, probably possessing functions distinct from those of the fibres of diiferent 

 structure. The latter is the view now adopted by the best anatomists. While it is 

 certain that elements of connective tissue exist in the nerves, and that these have been 

 mistaken for true nerve-fibres, there are in the nerves, particularly in those belonging to 

 the great sympathetic system, fibres exactly resembling the nerve-fibres of the embryon. 

 These are the true gelatinous nerve-fibres, or fibres of Remak. It is stated that the 

 nerves generally have this structure up to the fifth month of intra-uterine life, and that, 

 in the regeneration of nerves after division or injury, the new elements assume this 

 form before they arrive at their full development. 



The true gelatinous nerve-fibres present the following characters : They are flattened, 

 with regular and sharp borders, grayish and pale, presenting numerous very fine granu- 

 lations, and a number of oval, longitudinal nuclei, a characteristic which has given them 

 the name of nucleated nerve-fibres. The diameter of the fibres is about y-fa-y of an inch. 

 The nuclei have nearly the same diameter as the fibres and are about J^TT f an inch 

 in length. They are finely granular and present no nucleoli. The fibres are rendered 

 pale by the action of acetic acid, but they are slightly swollen only, and present, in this 

 regard, a marked contrast with the elements of a connective tissue. The microscopical 

 appearances of these fibres, which are strongly characteristic, are represented in Fig. 175. 



Accessory Anatomical Elements of the Nerves. The nerves present, in addition to the 

 different varieties of true nerve-fibres just described, certain accessory anatomical ele- 

 ments common to nearly all of the tissues of the organism, such as connective tissue, 

 blood-vessels, and perhaps lymphatics, although these have never been demonstrated, 

 except in the nerve-centres. 



Like the muscular tissue, the nerves are made up of their true anatomical elements 

 the nerve-fibres held together into primitive, secondary, and tertiary bundles, and so 



