MINUTE ANATOMY OE THE PAPILLAE OF THE FROG'S TONGUE. 
447 
arrangement as I believe it to be in Plate XXI. fig. 6, from the central part of one of 
the hemispheroidal masses. I regard the entire hemispheroidal mass as resembling in 
its essential structure the network I have described at the summit of the papilla, but 
the masses of germinal matter are so very close together and the fibres so much interlaced 
with one another, that it is most difficult to unravel the mass without destroying it. 
The arrangement at the surface is seen in Plate XXI. fig. 7. 
The epithelium of the tongue generally is easily removed, but many of these hemi- 
spheroidal masses remain connected with the summits of the papillae to which they 
belong. From what I have stated, it will I think be admitted that the constituent 
parts of the mass at the summit of the papilla could not be properly called epithelial 
cells, so that, with reference to the termination of the nerves in the papilla, I think 
it is more correct to say that nerves may be traced to special bodies or cells which 
form a hemispheroidal mass attached to the summit of the papilla, than to assert that 
the separate bodies, which compose the mass in which nerves terminate, are actual 
epithelial cells. 
In the simple papillae (Plate XXI. fig. 1, d) of the frog’s tongue, a “nucleus” of a nerve 
sometimes projects beyond the outline of the papilla and lies amongst the epithelium. 
This nucleus, however, adheres to the papilla when all the epithelial cells have been 
detached. It might from its position be easily mistaken for an epithelial cell, but it is 
no more really related to this structure than is a ganglion-cell, or a caudate nerve-cell 
of the spinal cord. The cells of the ciliated epithelium of the frog’s tongue are not in 
any instance, as far as I am able to observe, connected with the nerve-fibres. It is 
probable that the opposite inference, which is still held by many observers, has resulted 
from the observation of such a nucleus as is represented in Plate XXI. fig. 1, d pro- 
jecting beyond and adherent to the surface of the papilla. It is really continuous 
with the delicate nerve-fibres ( e ) ramifying in the substance of the papilla, but it is not 
an epithelial cell, and remains adherent after every particle of epithelium has been 
removed. 
The nervous tissue is in all cases structurally distinct from every other tissue, in every 
part of its distribution. It never blends with epithelium any more than it blends with 
fibrous tissue, cartilage, bone, or muscle. If nerves exert any direct influenee upon 
the nutrition of any of these tissues, the influence must be exerted through some 
distance. The results of anatomical research render any physiological doctrine which 
maintains that nerves act through their structural continuity with other tissues unten- 
able. My own observations lead me to conclude that nerves do not directly influence 
the processes of nutrition, growth, or development at all. They act only indirectly, and 
affect the supply of nutrient matter distributed by modifying the calibre of the vessels, 
and hence regulate the supply of blood which passes to the capillaries. The nerves 
I believe really exert their influence upon the contractile muscular coat of the small 
arteries and veins alone, and do not act directly upon any other tissues. 
