384 H. E. JORDAN 



capillaries end abruptly upon the surface of the enamel organ; 

 they nowhere penetrate the stellate reticulum. Occasionally 

 the condition may be seen in sections where a capillary has 

 indented the outer surface of the enamel organ and is then con- 

 tinued along the surface vertically for a long distance, following 

 various irregularities of the outer tunic (fig. 2). The picture 

 suggests a process of deflection of a blood vessel met with the 

 resistance of an opposing obstacle. Occasionally one sees what 

 appears to be a blood vessel within the outer border of the 

 enamel pulp. When such a vessel is carefully traced, however, 

 it becomes clear that the vessel has not actually penetrated the 

 enamel organ, but has simply pushed itself into the periphery, 

 carrying the outer tunic before it. Blood vessels do not invade, 

 but simply invaginate, the peripheral surface of the enamel organ. 

 The extensive network of extrinsic capillaries in their ramifica- 

 tion over the surface of the enamel organ, and pressing upon the 

 outer tunic, becomes so intimately blended at certain points 

 with the outer enamel epithelium that the endothelium and the 

 enamel cells become fused into a continuous membrane. Indeed, 

 probably also chiefly through the operation of the factor of 

 mutual pressure, the outer enamel epithelium and the mesenchy- 

 mal cells of the dental sac also become continuous. Where the 

 endothelium of the terminal capillaries and the cells of the outer 

 enamel epithelium fuse, opportunity is offered for blood cor- 

 puscles to pass into the outer border of the enamel organ, 

 mainly into the meshes between the outermost border of the 

 stellate reticulum and the outer enamel epithelium. Such cor- 

 puscles then come to lie free in the intercellular spaces. But 

 neither the capillary wall itself nor the capillary lumen as such 

 is continued into the enamel organ. The presence of such isolated 

 red blood corpuscles in the peripheral portions of the enamel 

 germ has no doubt given rise in part to the erroneous interpreta- 

 tion of intra-amelopulpar capillaries. The observation of such 

 intercellular corpuscles and of invaginated blood vessels (giving 

 the appearance of intrapulpar vessels in certain sections) has 

 led to the mistaken impression that blood vessels penetrate the 

 enamel organ. The intercellular blood corpuscles of the enamel 



