TISSUES OF THE BODY. 333 



membrane of the human larynx. Kisselcff appears to have seen similar 

 things in the mucous membrane of the frog's bladder, and recent investiga- 

 tions by Morano, Klein, Elin, and Chrschtschonovitsch, show that the same 

 arrangement of non-medullated filaments exists in the epithelium of the 

 conjunctiva, mouth, and of the vagina, sometimes with, sometimes with- 

 out the corpuscles of Langerhans. 



The mode of termination of the nerves in the pulp of the teeth (already 

 mentioned, p. 269), has also been recently followed up. 



Nervous twigs have long been known to exist in the walls of this struc- 

 ture. They may be easily seen here, and consist of dark-bordered fibres 

 whose diameter is 0'0038-0'0067 mm. These run upwards parallel to 

 each other, and then form an elongated nervous network by the branching 

 of their fasciculi. 



By the binary subdivision of these nervous twigs immense numbers of 

 very delicate silky primitive fibrillse are formed, according to Boll, which 

 resemble elastic fibres in some degree, but which are never seen to join in 

 a reticulated manner. These pass in between the odontoblasts (p. 270) to 

 reach the inner surface of the dentine, where they probably sink into the 

 dental canaliculi. Thus the latter contain a double system of fibres, 

 composed partly of Tomes' dental fibres (p. 270), and" partly of these 

 nerve fibres. The well-known sensitiveness of the tooth depends upon 

 the latter. 



188. 



We now turn to one of the most difficult subjects in nervous histology, 

 and one which is still the theme of much controversy namely, the struc- 

 ture of the ganglia. 



In regard to the relation of the nerve fibres to the cells even in the bodies 

 of fishes, where research is attended with least difficulty, considerable differ- 

 ence of opinion still exists. But this is the case to a far greater extent in 

 man and the higher vertebrates, where the difficulty of obtaining good 

 and serviceable objects is very great. Besides, it would be hardly prudent 

 to make use here of analogy to too great an extent, and to apply those 

 discoveries, which have been made in the body of the fish, to the human 

 organisation without due caution, in that we are not able to estimate, 

 with any certainty, the whole physiological connection between nerve 

 fibres and cells in general. On the other hand, it is no less dangerous to 

 take isolated observations, which have been with difficulty made on the 

 human and mammal body, and, generalising from these, to dash off with 

 bold strokes plans of the organisation of the nervous knots, which dazzle 

 us for a time by an apparent physiological consistency, it is true, but 

 which may be subsequently recognised as entirely incorrect. 



At first sight we recognise investing the nervous ganglia an envelope of 

 connective-tissue of varying thickness, a modified perineurium, consisting 

 partly of fibrillated connective-tissue alone, and partly of the latter inter- 

 mixed with Remaps fibres. This fibrous mass, in which the blood-vessels of 

 the ganglion are situated, extends also into the interior of the organ, which 

 is, however, 'chiefly made up of ganglion cells packed closely together. 



The nervous trunk or trunks entering the knot (fig. 319, b) are divided 

 in the latter into fasciculi, which conduct themselves in various ways. 

 Some of them, namely, traverse the structure directly, or with but little 

 deviation from the straight line (k), while others are resolved into primi- 

 tive fibrillse (/), which continue their course through the ganglion, twist- 



