STRUCTURE OF NERVOUS TISSUE. 341 



animals. 1 As yet, nothing is certainly known of the purposes to which these 

 different modes of connection are respectively subservient. 



343. The mode in which the Nerve-fibres terminate, at their peripheral 

 extremities, seems not to be always the same. It has been already shown that 

 the motor fibres, which are distributed to the muscles, have no proper termina- 

 tions; a series of loops, returning into themselves or joining others, being formed 

 by the ultimate ramifications of the main trunks ( 309). These loops in Man 

 seem to be formed by complete tubular fibres; but in some of the lower animals 

 (as the Frog), the "axis-band" seems to pass beyond its envelops, and to split 

 up into more minute fibrillae. So in the tactile papillae of the Human Skin, the 

 looped termination of the fibres (Fig. Ill) can ordinarily be well made out by the 



Fig. 111. 



Distribution of the Tactile Nerves at the extremity of the Human Thumb, as seen in a thin perpendicular 



section of the skin. 



method described by Prof. Kolliker ( 239) [Dr. Rudolph Wagner has recently 

 been making the distribution of the nerves in the skin of the tactile extremities of 

 the fingers his peculiar study, and has communicated the following results of 

 his inquiries to the Royal Society of Glottingen. What are usually called the 

 tactile papillae are of two kinds namely, vascular papillae, which only contain 

 capillary loops; and nervous papillae, which are placed between them. These 

 last have a conical form; and each of them contains in its interior a peculiar 

 corpuscle, also of conical form, which receives the finest of the nervous fibrils 

 that enter the papilla. Each primitive nerve-fibre divides into a great number 

 of smaller branches, to which these tactile corpuscles are attached; and thus 

 each is connected with several corpuscles. It is further considered by Wagner, 

 that each single fibre conducts the impressions made upon any of these branches 

 to a certain spot in the nervous centres ; and that thus but a single sensory im- 

 pression is produced, whether the corpuscles supplied by any one fibre are touched 



1 Certain observations which have been made upon the nervous system of foetuses, in 

 which the brain and spinal cord were wanting, confirm the idea that this is one of the 

 modes in which the nerve-trunks come into connection with their ganglionic centres. The 

 nervous cords were for the most part developed ; and at their (so-called) origins or central 

 extremities, they were found to hang as loose threads in the cavities of the cranium and 

 spine. On examining these threads, it was found that the nerve-tubes, of which they con- 

 sisted, formed distinct loops ; each of which was composed of a fibre that entered the 

 cavity, and then returned from it. These loops were imbedded in granular matter, re- 

 sembling that interposed between the vesicles in the cortical substance of the brain, and 

 perhaps to be regarded as vesicular matter in an early stage of its formation. All that is 

 known of the laws of formation of such irregular productions, leads to the belief that we 

 may rightly consider this arrangement of the nerve-tubes as one which exists in the nerv- 

 ous centres, when they are normally developed. (See Dr. Lonsdale, in "Edin. Med. 

 and Surg. Journal," No. 157 ; and Mr. Paget in "Brit, and For. Med. Review," No. 43, 

 p. 273.) 



