No. 9. — The Superior Incisors and Canine Teeth of Sheep. By 



Florence Mayo.* 



In 1839 Goodsir (p. 83) stated that " the cow and sheep, and prob- 

 ably all the other ruminants, possess the germs of canines and superior 

 incisives at an early period of their embryonic existence." 



This statement remained imdisputed until 1873, when Pietkewickz 

 (p. 509) denied the existence not only of the teeth germs, but also of 

 the so-called dental lamina. He says : " Dans une longne serie de 

 preparations faites sur des embryons de boeuf et de mouton, pris depuis 

 le moment le plus recule de la vie embryonnaire jusqu'a une longuer de 

 30 centimetres, non seulement je n'ai jamais constate la presence de 

 follicules, mais je n'ai meme jamais trouve trace de la lame epitheliale." 



Legros and Magitot('73, p. 452) content themselves with simply quot- 

 ing the results attained by Pietkewickz, but add nothing of their own. 



Somewhat later, Piana ('78, p. 222) asserts that the epithelial lamina 

 of the upper jaw extends to the region where the lateral incisors ought 

 to develop, and that the enamel germs of the canine teeth exist at a 

 certain stage of development, but soon abort. 



Pouchet and Chabry ('84, p. 158), calling the canine tooth the fourth 

 incisor, admit the existence of a dental lamina in the region of the 

 upper jaw, which is directly over the second incisor of the lower jaw, 

 but claim that in front of this point it becomes gradually merged into 

 the crest of the plunging wall. They add : " Ainsi non seulement la 

 region incisive des ruminants ne presente aucun vestige de dents, con- 

 trairement a ce qu'on avait cru jL une certaine epoque, mais elle ne pos- 

 sede pas meme de lame dentaire differentiee, dans toute son ^tendue." 



In view of these conflicting statements and the theoretical interest of 

 the questions involved, further studies upon the subject are desirable. 

 Therefore, at the suggestion of Prof. E. L. Mark, and under his direc- 

 tion, I have undertaken to re-examine the development of the teeth in 

 sheep embryos of different ages, hoping to be able to add something tc 

 what was already known. My observations are as follows : — 



* Contributions from the Zoological Laboratory of the Museum of Comparative 

 Zoology at Harvard College, under the Direction of E. L. Mark. — No. XIII. 



VOL. XIII. — NO. 9. 16 



