308 Ilcrr Paul FreunJ on the Development 



later than i. 1 and /. 2. From my own experience I have 

 notliing to add to these statements, since the rudiment of i. 3 

 (the permanent /. 2) in the largest embryo examined by me 

 (10 centim. in total length) was but little further developed 

 than in tlie embryo from wliich fig. 20 of tlie French autliors 

 is derived. The rudiment of this tooth was represented by a 

 clavate enamel-organ, indented only by quite a flat papilla, 

 and situated ventrally and posteriorly to the greatly developed 

 deciduous i. 2. As stated by Pouchet and Chabry, /. 2 and 

 i. 3 lie in one and the same alveolus. 



As Fleisehmann convinced himself from the examination 

 of transverse sections, the di. 2 are enamel-crowned teeth 

 with two roots of dentine. 



In the mandible the rudiment of only one large incisor is 

 formed. In addition to this, however, Pouchet and Cliabry 

 discovered in Lepiis two new deciduous teeth, which are 

 situated in botli jaws in front of the large i. 1. They found 

 tliese teeth in embryos measuring from 28 to 45 millim. in 

 length, and in a rudimentary condition, to which nothing 

 analogous is known in otlier Vertebrates. Tlie abridged 

 account of their discovery runs somewhat as follows : — In 

 embryos measuring from 28 to 45 millim. and something over 

 in total length, there is found in front of the well-developed 

 enamel-organ of the large incisor, and in direct connexion 

 with its anterior face, an epithelial mass, which, in a cavity 

 Avliicli is completely closed towards the exterior, contains a 

 thimble-shaped cusp of dentine. The innermost columnar cells 

 of the c])ithclial sac stand directly upon the surface of this 

 cusp, and its pulp-cavity is filled with a certain number of 

 blood- corpuscles and embryonic cells. The enamel-organ (for 

 tlie epithelial sac can be considered as nothing else) of this 

 dentine cusji is distinguished, according to the French authors, 

 on the one hand by its compact texture (the enamel-pulp is 

 absent), and on the other by the fact that it completely sur- 

 rounds the cusp. The enamel-organ is connected by a cord 

 of epithelium with the posterior side and the lower border of 

 the sunken epithelial wall (" mur plongeant "). (Such is the 

 term bestowed by these authors upon the sunken epithelial 

 masses, which are found in many embryos in the region of 

 the future groove between the lip and the alveolar margin. 

 Projecting masses of epithelium, to which the authors apply 

 the term " mur saillant," correspond approximately to the 

 thickenings of the epithelium of the oral cavity at the edge of 

 the jaw, which Germans call the jaw-wall [KieferwallJ.) — 

 Our cusp of dentine disajipears long before birth, since it is 

 either absorbed or drops out. According to Pouchet and 



