TRANSACTIONS OF THE SECTIONS. S3 



in the foetus of the Balcena Mysticetus, a fact which has been verified 

 by Dr. and Mr. Frederic Knox, in whose museum there is a prepara- 

 tion exhibiting the germs under the form of sacs and pulps. Although 

 the germs never arrive at this stage of perfection in the cow and 

 sheep, they are yet distinct enough to indicate their existence ; and 

 the author of this paper has no doubt, that when the embryos of other 

 partially or wholly edentulous mammals have been examined, similar 

 results will be obtained. The author then proceeded to state, that the 

 peculiar maimer in which the sac of a ruminant molar, and probably 

 of every other composite tooth, is formed, may be best seen in longi- 

 tudinal or transverse sections of the sac and pulp of the fourth per- 

 manent molar of the sheep or cow. The internal surface of the cavity 

 of reserve is seen to end in a fold or folds ; when these meet, they 

 begin to curve towards the papilla, and to enter parallel to one another 

 the cavity or notch which is simultaneously forming in the latter. As 

 soon as the edges of the folds meet, the granular matter denominated 

 enamel pulp by Hunter (the formation of which was described by 

 Mr. Goodsir in the human embryo, at the last Meeting of the Associa- 

 tion,) begins to be deposited, cementing together the opposing folds, 

 sealing up the new sac, separating it from the rest of the cavity of 

 reserve, filling up the space existing between the pulp and sac, and 

 ultimately assisting in the formation of the depending folds of the 

 latter. The author then referred to the distinction which must be 

 draw^n between those permanent teeth, which are developed from the 

 primitive, and those which are developed from the secondary groove ; 

 and stated that he had been in the habit of dividing the teeth of these 

 animals, the dentition of which he had examined, into three classes ; 

 viz. 1. Milk or primitive teeth, developed in a primitive groove, and 

 deciduous. 2. Transition teeth, developed in a primitive groove, but 

 permanent. 3. Secondary teeth, developed in a secondary groove, and 

 permanent. Mr. Goodsir expressed a hope that other anatomists would 

 verify and extend this line of research, as the results appeared to him 

 not only confirmatory of certain great general laws of organization, 

 but as leading, in his opinion, by the only legitimate path, to the deter- 

 mination of the organic system to which the teeth belong, (a subject 

 exciting great interest at present,) and as it might enable us, in inves- 

 tigating the relations of dental tissue to true bone, to avoid the error 

 of confounding what there appears to be a tendency to do, analogy 

 with affinity. The paper concluded with a recapitulation of the prin- 

 cipal facts contained in it. 1 . In all the mammalia examined, the fol- 

 licular stage of dentition was observed. 2. The pulps and sacs of all 

 the permanent teeth of the cow and sheep, with the exception of the 

 fourth molar, are formed from the minor surfaces of cavities of reserve. 



3. The depending folds of the sacs of composite teeth are formed by 

 the folding in of the edges of the follicle towards the base of the con- 

 tained pulp, the granular body assisting in the formation of these folds. 



4. The cow and sheep (and probably all the other ruminants,) possess 

 the germs of canines and superior incisives at an early period of their 

 embryonic existence. 



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