TERMINATIONS OF THE SENSORY NERVES. 



515 



the skin on the middle of the sole of the foot. In the skin of the fore-arm 

 the corpuscles are very rare. According to Kolliker, the tactile corpuscles 



FIG. 180. Papillae of the skin of the palm of the hand (Sappey). 



1, papilla with two vascular loops ; 2, papilla with a tactile corpuscle ; 3, papilla with three vascular 

 loops ; 4, 5, large, compound papillae ; 6, 6, vascular net-work beneath the papillae ; 7, 7, 7, 7, vascular 

 loops in the papillae ; 8, 8, 8, 8, nerves beneath the papillae ; 9, 9, 10, 11, tactile corpuscles. 



usually occupy special papillae which are not provided with blood-vessels ; so 

 that the papillae of the hand may be properly divided into vascular and 

 nervous. 



The form of the tactile corpuscles is oblong, with their long diameter in 

 the direction of the papillae, Their length is -3^-3 to ^-$ of an inch (66 to 

 100 /A). In the palm of the hand they are ^ to rirr ^ an i ncn (100 * 

 165 ft) long, and -fa to -g-j^ of an inch (45 to 50 /A) in thickness. They gen- 

 erally are situated at the summits of the secondary eminences of the com- 

 pound papillae. They consist of a central bulb of homogeneous or slightly 

 granular connective-tissue substance, harder than the central bulb of the 

 corpuscles of Vater, and a covering. The covering is composed of connect- 

 ive tissue with a few fine elastic fibres. One, two, and sometimes three or 

 four dark-bordered nerve-fibres pass from the subcutaneous nervous plexus 

 to the base of each corpuscle. These surround the corpuscle with two or 

 three spiral turns, and they terminate by pale extremities on the surface of 

 the central bulb. 



End-Bulbs. Under this name, a variety of corpuscles has been described 

 by Krause, as existing in the conjunctiva covering the eye and in the semi- 

 lunar fold, in the floor of the buccal cavity, the tongue, the glans penis and 

 the clitoris. They bear some analogy to the tactile corpuscles, but they are 

 much smaller and more simple in their structure. They form rounded or 

 oblong enlargements at the ends of the nerves, which are composed of homo- 

 geneous matter with a delicate investment of connective tissue. They meas- 

 ure TisVo to ^iir f an i ncn (25 to 100 /A) in diameter. In the parts provided 

 with papillae, they are situated at the summits of the secondary elevations. 

 The arrangement of the nerve-fibres in these corpuscles is very simple. One, 

 two, or three medullated fibres pass from the submucous plexus to the cor- 

 puscles. The investing sheath of the fibres is here continuous with the con- 

 nective-tissue covering of the corpuscle, and the nerve-fibres pass into the 

 corpuscle, break up into two or three divisions, and terminate in convoluted 



