426 SPECIAL HISTOLOGY. 



many others. My reasons are the following : 1. The " fibres of Remak," 

 as may be easily shown, arise from the sheath of the nerve-cells of the 

 sympathetic ganglia, and are continued in the nervous trunks, surround- 

 ing the nerve-fibres arising from the ganglia. Now as it is certain that 

 these sheaths are a sort of connective tissue, as is apparent also from 

 the spinal ganglia, where they occur in precisely a similar way, only 

 more scantily and without their being continued into the nerves, it fol- 

 lows that the "fibres of Remak" can scarcely be anything else. 2. The 

 finest twigs of the spinal nerves also exhibit nucleated fibres, in all re- 

 spects like those of Remak, as for instance, those going to the skin, &c. ; 

 with respect to which, as they are wanting in the trunks of the nerves, 

 there can be no question at all of their not being nerve-fibres. 3. The 

 quantity of the "fibres of Remak" always diminishes towards the finest 

 ramifications, which could not be the case were they nerves. It is not, 

 indeed, altogether correct, as stated by Valentin, that they are not to be 

 found in the finer intestinal nerves, for there can be no doubt that they 

 do exist there, though much more rarely than in the trunks of the nerves, 

 and are only to be brought into view by compression. According to 

 Remak (Mull. " Arch.," 1844, p. 464), they also exist in the cardiac 

 nerves of the Mammalia ; although as far as I can perceive, only in the 

 immediate neighborhood of the ganglia. Relying upon these reasons, 

 I continue in the firm persuasion that the nucleated fibres in the sympa- 

 thetic nerve of adult Mammalia are a form of the neurilemma; but I will 

 not omit to remark, that I consider it quite impossible to determine, in 

 undeveloped nerves, what is neurilemma and what young nerve-fibres. 

 Thus in the Rabbit, 2-6 months old, in the n. caroticus internus, not a 

 single developed nerve-fibre is to be met with, and apparently nothing 

 but "fibres of Remak," although it is quite certain thattogether with 

 them, there must also exist the rudiments of numerous dark-bordered 

 fibres. In the nerves of the spleen, in the Calf, in like manner, nume- 

 rous nucleated fibres are met with, though in the terminations (vide 

 " Cyclopaedia of Anatomy," III. p. 795, figs. 539 and 540), which, pro- 

 bably, afterwards become nerve-fibres. In young animals, consequently, 

 we must not look for a decision of the question; whilst in older ones, it is 

 quite otherwise. In them, a nucleated fibre can only be regarded as 

 a nerve when it can be traced into a dark-bordered fibre, or to a true 

 process of a nerve-cell ; and this, as we have seen, is not the case in 

 those of the sympathetic system. It may, however, be remarked, that 

 " fibres of Remak" also occur in the ganglia of the main sympathetic 

 trunk, but that they do not, for the most part, extend to any distance 

 beyond them, so that usually but few are contained in the trunk of the 

 nerve itself, 



126. Development of the elements of the Nervous System. The 



