8 4 



this two branches are given off, pulpal processes communi- 

 cating with the branched cells of the pulp, and tubular 

 processes which enter the dentinal tubules. Sketch under 

 high power a portion of the pulp with odontoblasts and a 

 segment of the adjacent dentine. 



(c) Developing Tooth Showing the Enamel Organ. 



A cat embryo about an inch in length was hardened in 

 mercuric chloride. The head was removed and stained in Dela- 

 field's hsematoxylin, embedded in paraffin, and cro^s sections of the 

 face made. Fix and mount in balsam. 



Study first under low power. The preparation shows 

 the nasal cavities, separated from each other by the nasal 

 septum, and separated from the oral cavity by the roof of 

 the mouth. From the floor of the mouth there projects a 

 broad fold, the tongue. In the developing lower jaw will 

 be seen the enamel organs, a little to the side of the tongue ; 

 also, at a point just above, in the developing upper jaw. 

 Study one of the enamel organs under high power. It has 

 the shape of a shallow bowl, and is in connection with the 

 epithelium lining the mouth cavity by a narrow stalk. 

 The enamel organ is developed from this epithelium. The 

 embryonic connective tissue under the enamel organ shows 

 a denser structure, and much more cell proliferation than 

 the surrounding connective tissue; it constitutes the 

 dental papilla. Sketch the section in outline as seen 

 under low power, and one of the enamel organs and dental 

 papillae as seen under high power. 



(d) Developing Tooth Showing Formation of 



Dentine and Enamel. 



The head of an embryo cat (about 4 to 5 inches long) was 

 hardened in picro-sulphuric acid, stained in Delafield's hsematoxy- 

 lin, embedded in paraffin, cross-sections of the face made, fixed to 

 cover glasses, counter-stained in eosin, dehydrated, and cleared in 

 oil of bergamot and xylol. Mount on balsam. 



Study first under low power. The same general 

 structure will be recognized in this section as in (c) of this 

 lesson. Study one of the developing teeth under high 

 power. In the enamel organ three kinds of cells can be 



