62 PRACTICAL HISTOLOGY. 



ranine artery in any of the above sections. In the course of the lingual and glosso-pharyngeal 

 nerves, not unfrequently fine ganglia are seen. I have often seen them in sections, and 

 isolated them from these nerves (Remak, Kolliker, Stirling). 



TASTE-BULBS. The papillae foliatse on the sides of the back part of the rabbit's tongue 

 are hardened in the same way as the tongue. Make vertical sections through the leaflet-like 

 papillae. After staining them with logwood, mount in dammar. They are also found on the 

 circumvalate papillae, but the papillae foliatas are preferable. They are also found on the pos- 

 terior surface of the epiglottis. 



EXAMINATION (L). Observe the flattened papillae lying side by side ; and on each side 

 of a papilla the four oval or flasklike taste-bulbs. At the base of the papillae the ducts of 

 serous glands (p. 61) may be met with (PI. XII., Fig. 3). 



(H). Study a taste-bulb made up of narrow epithelial cells arranged like the staves of a 

 barrel, investing modified epithelial cells, each provided with a fine process, which projects 

 through an opening at the upper part of the investing cells (PI. XII., Fig. 4). 



The ' inner ' and ' outer ' cells may easily be isolated by teasing out a small piece of a 

 papilla, hardened in a quarter per cent, osmic acid solution. 



TOOTH. 



UNSOFTENED TOOTH. 



PREPARATION. The same as that employed for dense, dry bone (p. 33). It is better 

 to purchase a section ready-made than to spend time in grinding down a section. 



EXAMINATION of a vertical section (L). Observe the dentine or ivory forming the great 

 mass of the tooth and surrounding the pulp-cavity in the centre, the enamel covering the 

 crown and sides of the dentine and the crusta petrosa or cement, a layer of bone without 

 Haversian canals covering the fang. In the enamel are a number of concentric dark lines- 

 ' contour lines ' running across it. In the dentine, note the wavy lines and their varying 

 direction the dentinal tubules. They stand out clearly because they are filled with air. 

 Arched incremental lines may be seen running across the dentine. 



(H). Dentine. In the homogeneous matrix the dentinal tubules, which open by one end 

 into the pulp-cavity and run out with a wavy course through the dentine, dividing dichoto- 

 mously, and giving off many anastomosing lateral branches, end in the outer part of the 

 dentine, either in loops, or they open into irregular spaces the interglobular spaces. 



Cement or Crusta Petrosa. Like bone but without Haversian canals. Some of the lacunas 

 may open into the interglobular spaces. 



Enamel. Observe the transversely striated polyhedral prisms set in groups on the dentine. 

 If cut transversely, they are seen to be hexagonal. Not unfrequently cracks are seen in the 

 enamel where it rests on the dentine, and these cracks appear black from being filled with 

 air. 



SOFTENED TOOTH. 



PREPARATION. Take the lower jaw of a cat or dog, and carefully free it from its muscles, 

 but retain the periosteum. Cut it in pieces of an inch long with a saw, and place the pieces in 



