HISTOLOGY OF ENAMEL ORGAN 395 



up coincident with an invasion of capillaries from the dental 

 sac. As I have attempted to make clear in my description of 

 conditions relating to the blood supply of the enamel organ, 

 what actually occurs in the specimens of my sections is an inti- 

 mate fusion at certain points between the cells of the outer en- 

 amel epithelium and the endothelium of the capillaries. This 

 establishes a continuity between the lumen of the capillaries and 

 the intercellular spaces of the outer enamel epithehum, per- 

 mitting an infiltration of occasional red blood corpuscles. But 

 no capillaries can be found actually growing into the enamel pulp. 

 Areas giving the impression of intrinsic blood vessels are invaria- 

 bly found, on closer study, to represent transverse sections of 

 capillary loops invaginated into the surface of the enamel organ. 

 Such loops simply produce indentations of varying depth into 

 the outer surface; they are always separated from the stellate 

 reticulum, except for occasional restricted areas of fusion with 

 the cells of the outer tunic, by the intact outer enamel epithelium. 

 In other words, certain blood vessels may invaginate, but do 

 not actually pierce, the outer surface of the enamel organ. 



Hopewell-Smith ('18), while admitting that the external 

 enamel epithelium and the enamel pulp of the tooth of the kitten 

 lack blood vessels, claims nevertheless that one or two large 

 non-branching vessels traverse the pulp and advance as far as 

 the stratum intermedium where they 'suddenly break up into 

 numbers of small capillaries, and form a beautiful plexus which 

 supplies the cells of this intermediate layer and the internal 

 epithelium' (pp. 263, 264). The illustrations offered in support 

 of this description do not seem to me to warrant the interpretation 

 given. Analysis of these illustrations (figs. 227 and 229) reveal 

 that the capillaries end abruptly upon the outer enamel epithe- 

 lium in that portion of the enamel organ where the stellate 

 reticulum persists. Only over the coronal apex where the enamel 

 organ remains only as a very thin membrane, consisting merely 

 of largely spent ameloblasts and outer enamel epithelium, are 

 the blood vessels brought in close relation with what represents 

 the remains of the stratum intermedium. Here the enamel 

 organ is atrophic, the tips of certain of the capillaries have fused 



