JACUBOWITSCH, ON THE XERVOUS SYSTEM. 125 



dividing several times, turns upon itself among the blood- 

 vessels, and again quits the papilla, in order to join the 

 nervous plexus, which I am about to describe. 



c. The nervotis jjlexus is constituted in the following 

 manner; — The bundles of nerves with a double contour 

 (motile), as well as those with a simple contour (sensitive), 

 which run beneath the integument in various directions, 

 divide several times, and then their primitive fibres become 

 slenderer and slenderer, so that, at last, they come to resemble 

 axial cylinders, which are interlaced, so as to constitute a 

 true nervous plexus. The loops whicli enter the cutaneous 

 papillae, and which I have just adverted to, enter into the 

 composition of this plexus. I would designate this peculiar 

 distribution, this peripheral expansion of the motile and 

 sensitive nerves, under the name of peripheral capillary 

 nervous plexus. It corresponds, in all respects, with the 

 plexus which Ave find at the periphery of the cerebrum and 

 cerebellum, and must be regarded as a special peripheral 

 termination of the nerves. A similar condition of parts is 

 readily seen in the tongue and on the nipples ; on the one 

 the termination of the nerves of taste being in the nucleus of 

 nerve- cells, and in the other the peripheral capillary plexus 

 being continued into the muscles existing in the part. 



III. The retina. — The first and innermost layer is the peri- 

 pheral nervous expansion of the optic nerve, in which this 

 peculiarity may be remarked — that the nervous fasciculi end 

 in becoming confounded Avith the axial cylinders which ter- 

 minate in the nucleus of a nerve-cell. The second layer is the 

 cellular layer, properly so termed; it is formed of several 

 superimposed layers of cells. The form of these cells is more 

 or less rounded or oval, and they vary much in size. The 

 external and superior are the largest, Avhilst the inferior cells 

 are no bigger than the nuclei of those placed more super- 

 ficially. In this layer it may be seen how the axial cylinders 

 are curved at the horizontal surface, in order to reach 

 the neighbouring cells, and thence the more remote cel- 

 lular layers, until they attain to the third layer (nuclear 

 layer), which is next in order. With higher magnifying 

 powers there may be seen in this layer double nuclei, and 

 even farther subdivision of the nuclei, as has been also 

 noticed by other observers as well as by myself, at the 

 periphery of the cerebrum and cerebellum, and especially in 

 the optic thalarai. Prom this circumstance I have been led 

 to regard this last layer of the retina as the site Avhere the 

 evolution of the cells takes place, that is to say, as a situation 

 where the nuclei must be regarded as future nei've-cells, and. 



