174 H. SPENCER HAEEISON. 



already mentioned), wliicli are superposed on the dentai 

 laminfe in sncli a way as to lead to great difficulty in dis- 

 tinguishing the respective limits (see figs. 5, 8, m«n.lin.; 

 9, m. lin.; 14 and 19, lin. gr. and r. d. I.). As in the labio- 

 dental groove, the side facing the teeth is glandular. 



Lying between palatine and maxillary series is a ridge 

 similar to the others described (crista gingivalis media- 

 lis), and the internal face of the palatine is covered by 

 another ridge (crista gingivalis palatinte), the two 

 being connected anteriorly. The palatine has, therefore, 

 grooves on its outer and inner faces, and they are continuous 

 anteriorly. We may call these the internal and external 

 palatine fossas. The latter corresponds to the labio-deirtal 

 groove, and is formed from an independent ingrowth of the 

 epidermis (figs. 5 and 9, j). lah.), whereas the former is 

 developed from an ingrowth of cells bearing the same relation- 

 ship to the teeth and dental lamina as I have just described 

 in the case of the mandibular and maxillary lingual in- 

 growths. 



As in the two following stages it is not always possible to 

 distinguish between the dental laminfe and the supei-posed 

 ingrowths, I have made use of descriptive terms having no 

 morphological significance. 



Stage R— S. 



This embiyo was intermediate between the Stages R and S, 

 as defined by Dendy, and was 6*3 cm. in length. It was 

 found dead in the egg, and its preservation therefore leaves 

 something to be desired. 



In all three tooth-bearing regions there are now present 

 both external and internal (labial and lingual) epidermal 

 ingrowths, having extremely varying and perplexing relation- 

 ships to the enamel organs. It is no longer possible to 

 indicate with certainty any of the dental larainge, although 

 they are no doubt represented in the lingual strands 

 (fig. 8, man. lin.; fig. 9, m. lin., p. lin.). In some cases 

 these are attached to the lingual sides of the enamel organs 



