Herrick-Coghill, Nerve Endings in the Skin. 33 



proliferation, extend to the brain, there to enter into communi- 

 cation in the glomerules with the processes of the mitral cells 

 of the tuber. 



As studied in the embryos of snakes the process is as fol- 

 lows : The first indication of the change of the ordinary to the 

 sensory epithelium is seen in the thickening of a portion of the 

 superficial layer from the morphological front of the head (the 

 region of the future infundibular recess) in relatively broad 

 bands, one on either side of the head. As the head flexures 

 increase, these areas are carried ventrad and come to occupy the 

 roof of the mouth and adjacent parts of the buccal cavity. The 

 development of the taste buds from this epithelium we have 

 not traced in these subjects, though there is no reason to doubt 

 that they are formed from this proton, as it is easy to see that 

 the mucous part of the hypophysis is. At the time the first 

 olfactory rudiments appear, the curvature is such that the hem- 

 ispheres are protuberant in front and so come nearly in contact 

 with the prota of the olfactory in the two bands of germinative 

 epithelium above mentioned. Still there is no difficulty in see- 

 ing that the original proliferations take place in the skin and 

 that the constant proliferation by division of the earlier cells 

 spins the nerve fiber from the original source to the point where 

 the tuber subsequently arises. In fact, the tuber, which has 

 frequently been compared to the ganglion of origin of a cranial 

 nerve, does not seem to afford origin for any centrifugal fibers 

 whatever. In preparations by the silver method it is easy to 

 see that the neurite of the moniliform chain of the olfactory 

 nerve comes into relations in the glomerules with dendrites of 

 the mitral cells. Though a considerable wealth of detail has been 

 secured by study of Golgi preparations during the last few years, 

 nothing has been brought to light to invalidate our original 

 view. 



For a long time during the development of the brain an 

 obvious ganglionic mass lies below the skin at the base of the 

 point of origin of the olfactory. The gradual elaboration of 

 the cavities of the nares only serves to redistribute the prota 

 without materially disturbing the simplicity of the arrangement. 



