224 THE NERVOUS SYSTEM. 



forks, or at its distal extremity may end in a bulb or divide 

 into fibrils. The axis-cylinder is surrounded by a granular 

 or perhaps multinucleated substance, which forms a cylindri- 

 cal core or " inner bulb." 



The bulk of the Pacinian corpuscle is chiefly made up of a 

 series of twenty-five to fifty concentric lamellce, which envelop 

 the core. Each lamella consists of a delicate connective- 

 tissue membrane lined by endothelioid cells, the nuclei of 

 which appear prominently in sections. The lamellae are de- 

 rived, partly at least, from the perineurial sheaths of the 

 entering nerve-fibre, and they are separated by lymph-spaces 

 filled with serum. 



Taste-terminals : The taste-terminals are associated with 

 specialized neuro-epithelial structures in the tongue, the "taste- 

 buds" which are described at page 119. The nerves of taste 

 end in terminal fibrils which are distributed through the epithe- 

 lial lining of the mucous membrane in the vicinity of the taste- 

 buds ; some of the fibrils (intragemmal) ramify through the 

 taste-buds ; others (intergemmal) are distributed between them. 



Olfactory terminals : The olfactory nerve-terminals consist 

 of fine terminal fibrils distributed in the mucous membrane 

 lining the upper part of the nasal fossa?, in association with 

 specialized neuro-epithelial or neural elements, the " olfactory 

 cells," which are described on page 142. 



The Eye. 



The eye (Fig. 90) is a highly specialized camera-like organ 

 associated with the termination of the optic nerve. Its parts 

 are : the conjunctiva, the sclerotic coat and cornea (tunica 

 externa), the choroid coat, ciliary body and iris (tunica media 

 or uveal tract), the aqueous humor, the crystalline lens and sus- 

 pensory ligament, the vitreous body, the retina (tunica interna), 

 optic nerve, and certain subsidiary structures. 



The conjunctiva is a mucous membrane covering the front 

 of the eye and inner surface of the eyelids. It consists of a 

 tunica propria covered with stratified columnar epithelium, 

 except that over and near the cornea the epithelium is of the 

 stratified squamous variety and over the cornea there is no 

 tunica propria. 



