396 H. E. JORDAN 



with the outer enamel epithelium, and occasional blood cor- 

 puscles have infiltrated the intercellular spaces of the area repre- 

 senting the former stratum intermedium. But no capillary 

 endothelium has actually grown into this atrophic membrane. 



In the case of the tooth of the wallaby, Hopewell-Smith and 

 Tims ('95) make the still more positive statement that 'the abun- 

 dant evidence of blood vessels within the enamel organ is a very 

 striking feature.' They claim that blood vessels 'can be seen 

 entering the enamel organ apparently at more than one point 

 on the surface, and are often of sufficient size to clearly recognize 

 the blood corpuscles within them. They can be traced to a 

 point about midway between the outer and inner enamel epithe- 

 lium, but we have not seen them proceeding farther, neither 

 have we found them in the stratum intermedium, the position 

 in which they were described by the authors above mentioned' 

 (Poulton and G. B. Howes, in enamel organ of rat). They 

 think that 'it is extremely probable that the unusual vascularity 

 of the enamel organs in this animal (wallaby) is correlated with 

 the precocious development of the enamel'. 



But when one refers to their illustration of the tooth germs of 

 the wallaby (fig. 216, Hopewell-Smith), one sees little in support 

 of this statement. To be sure, some cellular mass, entering a 

 very short distance below the surface of the outer enamel epithe- 

 lium, and continuous with it, is labeled 'blood vessel.' But 

 there is nothing shown to prove that this single vessel has actually 

 pierced the outer enamel epithelium rather than having simply 

 pushed it ahead of itself a short distance into the stellate reticulum. 

 Even in the case of the enamel organ of the wallaby, where it 

 is claimed the clearest evidence of intrapulpar capillaries is 

 given, one can only remain skeptical about the actual presence 

 of intrinsic blood vessels. 



When one contrasts conditions in the dental pulp with those 

 in the stellate reticulum of the enamel pulp one is further im- 

 pressed with the meager evidence for the occurrence of blood 

 vessels in the latter. The mesoblastic dental pulp, in contrast 

 with the epiblastic enamel pulp, is extensively vascularized. 

 There is not the slightest difficulty in tracing, in sections, cap- 



