92 TISSUES OF THE NERVOUS SYSTEM. 



ment, in which the individual fibrils are distinctly woven to- 

 gether into a network. From the nerves of this plexus, fibrils 

 are given off either alone or in tufts. Their general direction 

 is towards the surface.' In taking this course they divide into 

 finer and finer filaments, so that the finest are scarcely dis- 

 tinguishable under the highest powers, and form, by repeated 

 anastomoses, a network which lies immediately under the epi- 

 thelium. The fibrils themselves are beset with minute granu- 

 lar varicosities. In either case these form a network, the 

 meshes of which are oblong or quadrangular. Corneas pre- 

 pared in the manner above described may be also advanta- 

 geously employed for the preparation of vertical and horizontal 

 sections. 



The nerves of the substantia propria of the cornea of the 

 frog are best demonstrated as follows: A silk thread having 

 been passed through the centre of the cornea of rana esculenta 

 and brought out again at the sclerotic ring, the two ends are 

 knotted together. After the thread has remained from five to 

 eight hours, the cornea is excised and placed for twenty min- 

 utes or more in half per cent, solution of chloride of gold. It 

 is then transferred to distilled water, and exposed to light until 

 it acquires a dark violet-red, or reddish-brown color; the time 

 required for this purpose varying from one to three days, ac- 

 cording to the season. The epithelium must now be removed 

 with the aid of sharp-pointed forceps, along with a veiy thin 

 layer ofcorneal tissue, after which the cornea is to be mounted 

 in glycerin. In such a preparation it is seen that the nerve 

 trunks form a rich plexus by division and anastomosis in the 

 corneal substance. The branches of this plexus may be dis- 

 tinguished as nerves or bundles of the first order, and resemble 

 in their structure the corresponding nerves already described in 

 the cornea of the rabbit. From these, smaller bundles, not pos- 

 sessed of a nucleated sheath (nerves of the second order) are 

 given off. These run a course which is sometimes winding, 

 sometimes straight, and are connected by scanty anastomoses, 

 so as to form a plexus of large meshes. They give off, either 

 laterally or terminally, the fibrils of the third order. 



Nerves of the Conjunctiva and Membrana Nicti- 

 tans. For the study of the nerves of the mammalian conjunc- 

 tiva, the conjunctiva fornicis, or the plica semilunaris of the 

 eye of the pig, calf, or rabbit answers best. Portions of the fresh 

 plica semilunaris are treated in the same way as the cornea of 

 the rabbit. As soon as the proper degree of coloration is at- 

 tained, the preparation is hardened in diluted alcohol. Sec- 

 tions are then made in both directions, and covered in glycerin. 

 The conjunctiva fornicis is prepared free over a considerable 

 surface, and spread out on a cork with the free surface up- 

 wards. It may then be immersed in gold solution in a cap- 



