608 PROCEEDINGS OF THE AMERICAN ACADEMY. 



methylene-blue preparations, and may be obser\efl in all l)rancbes of 

 dorsal nerves innervating deep-lying structures. It is entirely possi- 

 ble that structural distinctions will be established between the visceral 

 nerves to different organs. 



H. Sensory Endings of Dorsal Ncrrcs. 



This subject has long attracted investigators, and its study has 

 brought forth a great variety of opinion and suggestion. Quatrefages 

 ('45) described peripheral nerves ending in small ovoid bodies (the 

 corpuscles of Quatrefages), which he suggested represent special 

 mucous organs. Kowalewsky ('67) believed that the sensory nerves 

 end in epithelial cells. Owsjannikow ('68) occasionally saw what 

 appeared to be a nerve fiber connecting wdth a cylindrical epithelial 

 cell. He also noted what he calls a nerve-net, lying in the deepest 

 layer of the skin, a region well supplied with connective tissue. Reich- 

 ert ('70) describes certain cells in the epithelial layer of the skin, 

 which bear a spine-like external process. He designates these cells 

 as "thorn" cells. Langerhans ('76) found no branches uniting two 

 dorsal nerves, or any exchange of fibers. All dorsal nerves branch 

 in simple tree fashion. He believes that nerve plexuses are lacking 

 in all parts of the body, except at the mouth border. He found no 

 vestige of a fine end plexus such as INIarcusen describes, holding that 

 Marcusen was deceived by connective-tissue fibrillae. Langerhans 

 describes special small cells lying irregularly between the cylindrical 

 epithelial cells of the skin. These special cells have a small body and 

 large oval nucleus; they lack a cuticula (limiting or basement mem- 

 brane), and often possess a thread-like process at the internal end. 

 On the external surface each cell bears a long, stiff" hair, which some- 

 times has a thickened base. These special cells are particularly 

 numerous in the head region, but may be found on all parts of the 

 body. The hairs may be seen on living animals, but never show mo- 

 tion. The finer dermal nerve branches pass through small canals in 

 the so-called limiting membrane of the skin, each of which is located 

 where two small fissures in the membrane cross each other, usually 

 at right angles. After a short sub-epithelial course, these fibers unite 

 with hair-bearing cells, which Langerhans declares to be the endings 

 of the cutaneous nerves. These nerves are not in relation with the 

 ordinary epithelial cells, in fact; there are not enough nerve branchlets 

 to permit union with each such cell. 



Rohon ('82) states that the greater number of nerve branchlets run 



