375 



in a somewhat circular way. The structure bears a great resem- 

 blance to that described by Huber as the anläge of the pharyngeal 

 bursa (Fig. 10a, Huber). 



Of all the conditions described by writers, that shown by Mead 

 bears most resemblance to mine. 



Comparison of the tw^o diagrams. Fig. la and Fig. 6, suggests 

 that the posterior pharyngeal opening of the notochord has in 

 my embryo become obliterated, while the anterior one (A) persists 

 and the anterior detached remnant of notochord becomes specialised. 



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Fig. 5. High power. D Pharyngeal diverticulum. M Mesoderm. P Pharyngeal 

 epithelium. 



In the pig embryo described by Mead the notochord does not end in 

 the pharynx. It opens into the pharynx at (B) and leaves it again at 

 (A) to end blindly after running a short distance upwards towards the 

 base of the brain. This anterior part of the head chorda is exactly like 

 the condition in my specimen, but in the latter the main body of the 

 notochord though it bends downwards and ends close to the pharyngeal 

 wall (Fig. 1 b) does not actually open into it. Mead is considering the 

 development of the cranium and therefore does not give any opinion 

 as to what becomes of this anterior prolongation of the notochord. 

 In this connection I give two more quotations from Huber: 



