312 Heir Paul Freund on the Development 



fused in front witli tlie enamel- organ of tlie rudimentary tooth, 

 and beliind ])assos into the connective cord of i. 2, wliile, as 

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

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

 as has already been stated, highly complicated appearances. 

 What we have to remember is, that the enamel-organs of i. 1 

 and the rudimentary tootli are in direct continuity, wliile /. 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 lum])v, and when seen from the u))per side behind 

 somewhat flattened and indented. The margins of this hollow 

 subsequently become more decidedly elevated, and so assume 

 the characteristic bell-sha])e. 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. AVith 

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

 epithelial wall [mur plongeant) ^ which marks out the subse- 

 quent groove between the lip and the alveolar border, becomes 

 nuicli more strongly develoj)ed 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 rumj), already assumes the 

 well-known bell-shape, in the manner which lias 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 ap])ears as though 

 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, surrounded 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 tooth 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 (yhabry and Pouchct, but always remains in connexion 



