394 H. E. JORDAN 



cally in contact with these cells. But in other mammalian teeth, 

 where the stellate reticulum of the enamel germ is very extensive, 

 the question of the blood supply for the ameloblasts takes on 

 greater importance. For here the assumed nutritive materials 

 for the support of amelogenesis, in the absence of intra-amelopul- 

 par capillaries, must be transported by the agency of the cells of 

 the stellate reticulum across a considerable width. 



Skillen was unable to find, even in injected specimens, any 

 trace of blood vessels in the enamel pulp or surrounding the 

 stratum intermedium. He adds that Svhen the outer and inner 

 tunics come into apposition, thus forming the papillary layer, 

 the vessels accompany the outer tunic and so come to lie in the 

 portion described by Williams' (p. 3), that is, in the 'papillary 

 layer' and in close relation with the ameloblasts. It must be 

 remarked, however, that during the early stages of tooth devel- 

 opment, when amelogenesis is at its height, the outer and 

 inner tunics are still separated by a considerable area of stellate 

 reticulum. 



According to Noyes ('21), at about the time of the completion 

 of the dental sac ('follicle'), there appear on the outer surface 

 of the outer enamel epithelium ('tunic') small rounded pro- 

 jections of epithelial cells, and this layer becomes broken up 

 coincident with an invasion of capillaries from the dental 

 sac 'which carry the remains of the outer tunic down against 

 the inner tunic to form the stratum intermedium. There is an 

 intimate relation between capillary blood vessels and the stratum 

 intermedium' (p. 332). Noyes accordingly regards the stratum 

 intermedium as composed of pushed-in remains of the outer 

 enamel epithelium, and concludes that capillaries extend directly 

 into and through the enamel pulp ('stellate reticulum') to the 

 depth of the stratum intermedium. 



Aside from the fact that the stratum intermedium cannot be 

 correctly described as composed of pushed-in remains of the 

 outer enamel epithelium, I can find no evidence in my sections 

 of an actual invasion by capillaries of the stratum intermedium 

 or even of the stellate reticulum. Nor does it seem to me quite 

 accurate to say that the outer enamel epithelium becomes broken 



