— 84 — 



this two branches are given oflf, pulpal processes comimini- 

 cating with the branched cells of the pulj), nnd tubular 

 processes which enter the dentinal tubules. Sketch under 

 high power a portion of the pul|) with odontobhists and a 

 segment of the adjacent dentine. 



(c) Developing Tooth Showing the Enamel Organ. 



A cat embryo al)Oiit an iiicli in length \v:is hiinlpiir^d in 

 mercuric ciilorido. The liPiul was renioveil iiii'l staineil in Dela- 

 fiekl's IweinatoxyUu, emhclded in paratfiii, ami cross sections of tlie 

 face made. Fix and mount in balsam. 



Study first und^r low power. The preparation shows 

 tlie nasal cavities, separated from each other b\^ the nasal 

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

 the mouth. From the floor of the mouth there i)roiects a 

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

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

 abso, 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 develoi)ed from this epithelium. The 

 embryonic connective tissue under the enamel organ shows 

 a denser structure, and much more cell })roliferation than 

 the surrounding connective tissue; it constitutes the 

 dental ])apilla. 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 eml)ryo cat (about 4 to o inclies lon<r) was 

 hardened in picro-sulj)huric acid, stained in Dehifieid's hiematox\'- 

 lin, einbedde<l in paraffin, cross-sections of the face made, fixed to 

 cover t^lasses, counter-stained in eosin, dehydrated, and cleared in 

 oil of ber<^amot 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 



