382 H. E. JORDAN 



DESCRIPTION 



a. The enamel orgari of the kitten 



The teeth of kittens of the first three weeks are completely 

 covered by the enamel organ. Developmental conditions with 

 regard to the incisors, canines, and the premolar teeth are very 

 similar, and the following description applies in general equally 

 well to either of these teeth. There are minor differences, 

 especially with regard to the thickness of the enamel organ; 

 that of the incisor teeth is somewhat thinner than that of the 

 canines and premolars. Amelogenesis begins over the crest of 

 the crown and progresses towards the neck. The enamel organ 

 is accordingly more advanced in histogenesis over the coronal 

 apex. It follows, then, that the enamel organ over the coronal 

 parietes at any early stage of development represents an earlier 

 histogenetic stage as compared with the coronal apex and a 

 later stage as compared with the cervical and radicular portions. 

 The prenatal condition of the enamel organ over the coronal 

 apex may therefore be inferred from the postnatal condition of 

 the organ over the subcoronal portions of the tooth. It should 

 be emphasized that in the kitten's tooth the enamel organ envel- 

 ops practically the entire tooth, approximately to the level of 

 the primordium of the future foramen apicis dentis. Judging 

 from the published illustrations, a similar condition prevails 

 also at comparable stages in the teeth of man, sheep, dog, pig, 

 calf, and wallaby. A description of the enamel organ of the 

 kitten will therefore apply generally also to other large groups 

 of mammals. 



The enamel organ at this early postnatal stage is thickest in 

 a wide region between the coronal and radicular apices, that is, 

 in the region of the primitive neck (fig. 1). Here it consists of 

 an innermost layer of tall columnar cells, the ameloblasts, a wide 

 pulpar region or stellate reticulum, and a thin superficial layer 

 composed of cuboidal or squamous cells of an endotheloid charac- 

 ter (fig. 2). Between the layer of ameloblasts and the stellate 

 reticulum there occurs, more or less regularly, a thin layer of 

 closely packed small ovoid cells, the stratum intermedium. 



