546 Stewart Paton 



from a group of cells lying ventrally and in the periphery of the 

 brain pass backwards in the marginal veil, until they reach a point 

 just behiud wliicli the Trigeminus fibres first makc their appearance. 

 This nerve even at this early stage presents interesting features. 

 A eollection of pear-shaped cells lying in the outer margin of the 

 medulla are connected with fi bri 1 buudles uniting theni with the 

 mass of the Trigeminus ganglion. In each section, in this area 

 one meets with two or three of these cells, while within the ganglia 

 itself large numbers of rather thick deeply staiued fibrils, all practi- 

 cally runniug in the same direction towards the periphery ou the 

 one side and the medulla upon the other, are plainly visible. This 

 Observation does not confirm the affirmation of Klinkhardt (Kopf- 

 ganglien und Sinneslinien der Selachier. in: Jena. Zeit. Naturw. 

 40. Bd. 1905) to the effect that at this period the ganglion as far 

 as nervous connections are concerned, is isolated from the medulla. 

 Not only do central connections exist but the ganglion is also al- 

 ready intimately united with the inner surface of the epidermal 

 layer by neurofibrils which sometimes seem to form a loose plexus. 

 Often, however, the individuai fìlaments end abruptly and blindly 

 without penetrating further between the nuclei of this layer. 



It is not at ali improbable, as Guthke (Ganglien und Nerven des 

 Kopfes von Torpedo ocellata, in : Jena. Zeit. Naturw. 42. Bd. 1906) has 

 pointed out, that nuclei derived from the ectoderm enter the ganglion 

 thus forming, genuine connections with the periphery. 



The majority of fibrils are found in the ganglion in those 

 sections where it has attained its greatest dimensions, but only a 

 comparati vely few appear in the brauch to the ciliary ganglion. 



The brauch described both by van Wijhe and Guthke as 

 running perpendicularly to the course of the R. ophthalmicus profundus 

 and connecting the ciliary ganglion with tlie epidermis does not 

 yet contain any fibrils, although numerous protoplasmic Strands may 

 be Seen uniting the ganglionic mass with the periphery. A few 

 rather coarse deeply stained fibrils may, at this early stage, be 

 detected in the R. ophthalmicus jirofundus and are the first to 

 appear in the cross sections as we jiass from the head to the tail. 

 They curve inwards behind the eye to a point in the mesenchyme 

 where they can not be traced any further. Thus it will be Seen 

 that the whole tract of the Nervus ophthalmicus profundus is al- 

 ready practically diffcrentiated into fibrils. 



