TERMINATION OF NERVES. civ 



many cases, the fibre, before terminating, divides into two branches, as represented in 

 figure B : a division into three has been observed, but this is very rare. In case of 

 division of the fibre, the cavity is generally, but not invariably, divided in a corre- 

 sponding measure, and the inner set of capsules present a figure in keeping with it. 

 It is worthy of remark, that the nerve-fibre in its course along the cavity runs almost 

 exactly in the axis of the channel, and it maintains this position even when passing 

 through the abrupt flexures of an irregularly shaped cavity. It sometimes happens that 

 a fibre passes quite through one corpuscle and terminates in a second, resuming its 

 original size and dark outline while passing from the one to the other. Pappenheim 

 states that he has seen a nerve-fibre going through two Pacinian bodies without ter- 

 minating in either, but returning again to the parent nerve in form of a loop. Other 

 varieties occur, for an account of which the reader is referred to the several authorities 

 already mentioned. A little artery enters the Pacinian bodies along with the nerve, 

 and soon divides into capillary branches, which pierce the parietes of the passage and 

 run up between the capsules. Mr. Bowman finds that they then form loops, and 

 return by a similar route into a vein corresponding to the artery : he states also that 

 a single capillary usually accompanies the nerve as far as the central capsule, and 

 passes some way on its wall, sometimes in a spiral direction. 



There is considerable difference of opinion as to the condition of the nerve-fibre in 

 the Pacinian body. Kolliker thinks that it retains its primitive sheath, and is not 

 wholly deprived of its medulla ; and that the surrounding core is composed of a 

 nearly homogeneous connective tissue, in which he has seen faintly marked nuclei 

 and faint longitudinal striation. Engelmann, on the other hand, considers the core 

 to be an expansion of the medullary sheath of the nerve, and ascribes the appearances 

 noticed by Kolliker to changes occurring in the originally homogeneous medulla, 

 as in the case of a white nerve-fibre. The pale fibre within he considers to be simply 

 the axis-cylinder. The core and pale fibre of the end-bulbs he regards in precisely 

 the same way, and thinks it not improbable that the touch-corpuscles will be found 

 to conform. He looks upon the simple capsule of the end-bulb as a development of 

 the primitive nerve-sheath, to which, in the Pacinian bodies, is superadded a series of 

 concentric coats of connective tissue. Engelmann, besides adducing other arguments, 

 refers especially to the structure of the Paciniau bodies of birds, as affording material 

 evidence in support of his view. 



Nothing positive is known concerning the special purpose in the animal economy 

 which these curious appendages of the nerves are destined to fulfil. In an anatomical 

 sense a Pacinian body might be viewed as a more complex development of an end- 

 bulb, from which it differs chiefly in the multiplied layers of the capsule. W. Krause 

 endeavours to show that the series of concentric capsules with interposed fluid is an 

 arrangement for converting the effect of mechanical traction into fluid pressure upon 

 the nerve, so that tension and traction of the tissue in which the corpuscle is placed, 

 may be felt and appreciated as ordinary pressure. Their presence in the mesentery 

 of the cat seems, at first sight, against their importance as sentient organs, but it 

 turns out upon trial, that the part in question is remarkably sensitive. 



C. Other terminations of sensory nerves. 



a. In hair-follicle*. By far the majority of the nerves of the skin end in hair- 

 follicles. Up to their entrance, at least, they retain their dark borders, but their 

 arrangement within and actual mode of termination arc unknown. 



b. In the teeth. Dark bordered nerve-fibres, in fine bundles, enter the teeth and 

 pass into the tooth-pulp ; but their mode of termination has not been clearly made out. 



c. In organs of special sense. For the peripheral distribution of the optic and 

 acoustic nerves, and the elaborate apparatus in the eye and ear with which they 

 are connected, the reader is referred to the details given in the special anatomy 

 of these organs. Respecting the more simple termination of the olfactory nerve, 

 it has been shown by Max Schultze, that on the olfactory membrane, alongside 

 columnar epithelium cells, there are special nucleated cells of a fusiform shape, 

 and probably of a nervous nature (olfactory cells), from which proceed a superficial 

 and a deep process, often presenting a beaded appearance like varicose nerve-fibres. 

 The superficial processes end abruptly at the surface of the epithelium between the 

 columnar cells ; the deep and more slender processes pass vertically inwards. They 

 are probably continued from terminal fibres of the olfactory nerve, but the continuity 

 has not been actually traced. 



