412 INNERVAT10N. [CHAP. XIV. 



beneath the true skin, and separable from it; and we have observed 

 single tubules from the plexus penetrating this expansion in their 

 course to the skin. They have then been lost to view. We have 

 hardly been more fortunate in discovering the true termination of 

 the nerves in the nictitating membrane of the eye in the same 

 animal, or in the papillary tissue so largely developed on the 

 thumb at a certain season. 



In our attempts to follow the nerves for any distance under the 

 papillary structure in the higher animals, the fibrous tissues (and 

 especially the elastic variety), forming the cutis, have been found so 

 much to impede the view, that no satisfactory conclusion has been 

 arrived at. In regard to their presence in the papillae themselves, 

 we can affirm that we have distinctly traced solitary tubules 

 ascending among the other tissues of the papillae about half-way to 

 their summits, but then becoming lost to sight, either by simply 

 ending, or else by losing the white substance of Schwann, which 

 alone enables us to distinguish them in such situations from other 

 textures. Thin vertical sections of perfectly fresh specimens are 

 essential for this investigation, and the observer should try upon 

 them the several effects of acetic acid and solution of potass. In 

 thus describing the nerves of the papillae from our own observations 

 we do not deny the existence of true loop-like terminations as 

 figured by so respectable an authority as Gerber,* but neither do we, 

 feel entitled to assent to it. We have in numerous instances failed 

 to detect any nerves at all within the papillae, when such were 

 plainly visible at their base, and when, consequently, the chemic? 

 agent employed could scarcely have destroyed their characteristic 

 structure, had they been present. We incline to the belief that the 

 tubules either entirely or in a great measure lose the white sub- 

 stance when within the papillae. We would, however, refer the 

 reader to what will be found respecting the nerves of the papillae 

 of the tongue on the chapter on taste. 



The essential tissue of the papillae probably exists even where no 

 projections large enough to be called papillae are present. The* 

 portions of the skin are more scantily supplied with nerves ; and it 

 is probable from this circumstance, as well as from experimenl 

 afterwards to be detailed, that the individual nervous tubules 

 wider asunder, and occupy each a more extensive surface than in 

 parts thickly set with papillae. 



The cuticle, or epidermis (fig. 83, a), like the cutis, varies greatly 

 in its thickness. As its chief use is that of affording protection, it 

 attains most density on parts most exposed to pressure and friction, 

 * General Anatomy, translated by Gulliver. 



