18 



SPECIAL HISTOLOGY. 



papilla contains far less elastic tissue than the papilla fill- 

 formes , and it is almost wholly wanting in the secondary pa- 

 pillae ; on the other hand, a network of bundles of connec- 

 tive tissue of 0-002 — 0-003'" in breadth, is very distinct. The 

 vessels present the same arrangement as in the p. filiformes, 

 only that they are much more numerous; and as regards 

 the nerves, one or two larger trunks of 001 — 0'08'", enter 

 into every fungiform papilla, together with many minute 

 filaments, which, spreading out in the form of a brush, and 

 repeatedly anastomosing (see Zeitschrift fur Wiss. Zool., 

 Band IV, Tab. IV), finally diverge in all directions towards 

 the secondary papillae, and their axile corpuscles (see § 37). 



The nerves, which in the trunks measured 0002 — 0-004'", 

 on the average 0-003'", diminish in size during their course, so 

 that at the base of the papillae, their diameter is not more than 

 0-001 — 0-0015"', and they also exhibit distinct divisions ; I 

 have not yet observed their terminations with certainty, but 

 have thought that in some cases I could detect loops, in others, 

 free ends, without, however, pledging myself either to the one 

 or the other. 



In the papillae circumvallata the central papilla, which may 

 be regarded as a depressed papilla fungiformis, is closely covered 

 Fi 175 upon its plane terminal 



surface with simple co- 

 nical elevations, and is 

 invested externally by 

 an epithelium of uni- 

 form thickness, with- 

 out any special pro- 

 cesses and prolonga- 

 tions. The wall is a simple elevation of the mucous membrane, 

 possessing a smooth epithelial investment, beneath which its 

 upper border is produced into many rows of simple conical 

 secondary papillae. The elastic tissue is usually absent in the 

 papillae, otherwise, they have the same structure as the fungi- 

 form kind, only they are still mor^ abundantly provided with 

 nerves. Every proper papilla ch . u.mvaUata contains in its lowest 



Fig. 175. Papilla circumvallata of Man in section : A, proper papilla ; B, wall; 

 a, epithelium ; c, secondary papilla ; 6b, nerves of the papilla and of the wall ; 

 x about 10. 



