576 DBS. GEORGE AND FRANCES E. HOGGAN ON 



Mcmvier's S^ypotliesis of Direction of Groivth in Intraepidermic 



Nerves. 



At tlie conclusion of his article, " On the Terminations of the 

 Nerves in the Epidermis," in the ' Quarterly Journal of Microsco- 

 pical Science ' for 1880, Professor E^anvier gives out the following 

 hypothesis on the direction and growth of the intraepidermic 

 nerve-fibres, as borne out by the drawings by Karmanski of his 

 preparations from Man, the Pig, and the organ of Eimer in the 

 Mole. At page 458 he says : — " The nerves which enter the epi- 

 dermis, whatever may be the form or extent of their ramifications, 

 are subject to continuous evolution. They grow, while at the 

 same time their terminations undergo gradual degeneration ; this 

 degeneration leads to the formation of granules of nervous sub- 

 stance, which become entirely free, and are soon transported into 

 the inert layer of the epidermis." 



The above is merely an accentuation of Professor Eanvier's 

 views regarding nerve- development as expressed on page 75 of 

 the second volume of his excellent work, 'Logons sur I'histologie 

 du Systeme nerveux,' that the axis cylinders, forming as they do, 

 part of the nerve-cells in the central nerve-centres, develop cen- 

 trifugally from these centres. As far as the space between the 

 nerve-centres and the lower surface of the epidermis is concerned 

 we are quite in accord with him, but on arriving there our views 

 become divergent. 



A careful study of a very large number of preparations of all 

 the difiorent parts of many different classes of animals, leads us 

 to the conclusion that the great plexus or system of non-medul- 

 lated nerve-fibres and nerve-cells found immediately under the 

 epidermis is a system apart and quasi-independent of the central 

 nerve- systems. As the name and position of that plexus implies, 

 the direction of its fibres as regards the surfaces of the body is 

 lateral ; that is to say, the fibres run in a plane parallel to that 

 of the lower surface of the epidermis, as shown in fig. 28, Plate 

 XYI., which is a drawing from a silver preparation of the subepi- 

 dermic plexus of fibres and nerve-cells from the skin of the Hedge- 

 hog, shown from the plane of the outer surface of the epidermis. 

 On what may be called the central surface of this plexus, nume- 

 rous meduUated nerves join it (w, fig. 28), and thereby bring it 

 into connexion with the central nerve-centres ; but we hold that 

 anatomically these meduUated nerves terminate in the plexus ; 

 and on joining it, their peripheral direction of growth, in which 



