146 MICROSCOPIC ANATOMY OF THE TEETH 



above, that the external epithelium in man is in many 

 places discontinuous, and blood-vessels lie in direct contact 

 with the cells of the stellate reticulum (see fig. 70). It has 

 been demonstrated in many instances that beyond all doubt 

 blood-vessels do penetrate the external epithelium, and are 

 seen within the stellate reticulum of marsupials. 



Mr. Thornton Carter says that in marsupials the ramifica- 

 tions of these vessels extend often as far as the stratum 

 intermedium, but his fig. 21 is from a transverse section, 

 and does not show to what depth this vascular network 

 penetrates. He states, however, that in his preparations 

 vessels are frequently seen * in contact with the cells of the 

 stratum intermedium ' (5 a). 



They do not, however, form any regular system in this 

 situation, but are irregularly scattered in the reticulum, and 

 suggest that they show a vestige of an earlier condition in 

 which the presence of blood-vessels in the enamel organ 

 was a more constant and regular phenomenon, and the 

 condition gives rise to more interest in view of the observa- 

 tions of the author in recent investigations on the enamel 

 organs of the Sparidse and Labridse, to be presently referred 

 to, where a regular system of blood-vessels is seen in the 

 enamel organ, and where it evidently takes a very important 

 part in the calcifying functions. 1 



If we agree with the statement of Rose (21) that the 

 development of the stellate reticulum is intimately associated 

 with the deposition of a thick enamel cap in the higher 

 vertebrata, we must assign to this layer an important 

 function in the process of calcification, and it is considered by 

 Rose that the arrangement of the cells favours osmosis and the 

 conveyance of nutriment to the growing cells of the internal 

 layers ; it may also assist in the separation of calcifying 

 salts from the blood circulating in the vessels of the capsule. 



The stratum intermedium, which is in intimate relation 

 with the cells of the stellate reticulum, their processes com- 

 municating with one another, was considered by many to 

 be the recuperating layer for the cells of the internal epithe- 

 lium or ameloblasts ; but after the formation of enamel has 



1 In Pseudoscarus, which is very closely allied to the Labridae, blood- 

 vessels also penetrate the enamel organ. 



