312 Hen* Paul Freund on the Development 



fused in front with the enamel- organ of the rudimentary tooth, 

 and beliind passes into the connective cord of i. 2, while, as 

 we shall see, the latter is prolonged backwards into the dental 

 fold of the diastema. This, together with the steps, produces, 

 as has already been stated, highly complicated appearances. 

 "What we have to remember is, that tl)e enamel-organs of i. 1 

 and the rudimentary tooth are in direct continuity, while i. 1 

 and {. 2 are united by a structure which may well be regarded 

 as a dental fold. The epithelial mass of the enamel-organ of 

 i. 1 itself is lumpy, and when seen from the upper side behind 

 somewhat flattened and indented. The margins of this hollow 

 subsequently become more decidedly elevated, and so assume 

 the characteristic bell-shape. The enamel-organ of i. 2 is, as 

 may be seen from fig. 13, in not nearly so developed a con- 

 dition. 



We will here at once mention the changes which take 

 place in the region of the incisors in subsequent stages. With 

 reference to the lower jaw we have to observe tliat the sunken 

 epithelial wall {mur p/ongeant) , which marks out the subse- 

 quent groove between the lip and the alveolar border, becomes 

 much more strongly developed and extends further back- 

 wards. In the foremost sections it appears as a bifurcate 

 and deeply sunken epithelial mass, which to a certain extent 

 ensheaths the anterior end of the Meckelian cartilage and the 

 covering bones lying thereon. On the inside of the epithelial 

 mass is attached the common connective cord of the enamel- 

 organs of the rudimentary tooth and of the large incisor. The 

 latter in embryos measuring 1*5 centim. in cephalic length and 

 about 4 centim. from crown to rump, already assumes the 

 well-known bell-shape, in the manner which has been indi- 

 cated above. Since the size of this bell, which is enormously 

 expanded behind, and within which the tooth develops in the 

 usual way, by far preponderates, it now appears as thougli 

 the tip of the rudimentary tooth were implanted in the cord 

 connecting this great bell with the epithelium of the oral 

 cavity, while only the lower end of the tooth, suri'ounded by 

 its enamel-organ, projects freely downwards in front of the 

 great bell. The conditions which are now present are conse- 

 quently similar to those which are shown in fig. 14 in the 

 case of the squirrel. The rudimentary tootli is indeed far 

 behind the large incisor in growth, but nevertheless in older 

 animals, e. g. in rabbits measuring about 2'5 centim. in 

 cephalic length and circa 7 centim. in all, it has decidedly 

 increased in size in comparison with the younger stages. Its 

 pulp-cavity is never closed towards the exterior, as is stated 

 by Chabry and Pouchet, but always remains in connexion 



