74 



CELL DIFFERENTIATION AND THE ELEMENTARY TISSUES 



layer being lined by endothelium, figure 100. A single nerve fiber passes 

 through its pedicle, traverses the several concentric layers, enters a central 

 cavity, and terminates in a knob-like enlargement or in a bifurcation. 

 The physiological import of these bodies is still obscure. 



FIG. 100. 



FIG. ioi. 



FIG. ioo. Pacinian Corpuscle of the Cat's Mesentery. The stalk consists of a nerve fiber, n, 

 with its thick outer sheath. The peripheral capsules of the Pacinian corpuscle are continuous 

 with the outer sheath of the stalk. The intermediary part becomes much narrower near the en- 

 trance of the axis-cylinder into the clear central mass. A hook-shaped termination with the end- 

 bulb, a, is seen in the upper part. (Ranvier.) 



FIG. ioi. Summit of a Pacinian Corpuscle of the Human Finger, showing the Endothelial 

 Membranes Lining the Capsules. X 220. (Klein and Noble Smith.) 



The Tactile Corpuscles of Meissner. They are found in the papillae 

 of the skin of the fingers and toes, or among its epithelium. When simple 

 they are small, slightly flattened transparent bodies composed of nucleated 

 cells enclosed in a capsule. When compound, the capsule contains several 

 small cells. The nerve fiber penetrates the corpuscles, loses its myelin 

 sheath, and divides and subdivides to form a series of arborizations. The 

 terminal arborizations occupy the central part of the corpuscle, and are 

 surrounded by a great number of marginal cells. The touch or tactile 

 corpuscles of Meissner have been regarded at one time as epithelial, at 

 another time as nervous, but they are to-day proved to be mesodermic cells, 

 and differentiated for the special purpose of the sense of touch (Dejerine). 



The Corpuscles of Krause or End-Bulbs. These exist in great 

 numbers in the conjunctiva, the glans penis, clitoris, lips, skin, and in tendon 

 of man. They resemble the corpuscles of Pacini, but have much fewer 

 concentric layers to the corpuscle, and contain a relatively voluminous central 



