'673 



arises from the contact of the notochord with the pharyngeal wall and 

 consequent pulling of the wall, at a point posterior to and unconnected 

 with Seessel's pocket. The latter is the actual anterior end of the 

 notochord. He says: 



"The material presented, it seems to me, shows conclusively 

 that there exists in human embryos a distinct relation between the 

 head notochord and the pharyngeal entoderm in the development of the 

 pharyngeal bursa. In embryos having h. b. length of from 5 mm 

 to 8 mm, a time when the head chorda is separated distinctly from 



Fig. 2. 



Fiff. 3. 



Fig. 2. A Internal carotid artery. B Floor of 4th ventricle. P Pharynx. 

 P.B. Pharyngeal recess. T Tongue. F Anterior cardinal vein. 



the pharyngeal entoderm, one may determine a small area in which 

 the notochord remains in close contact with the pharyngeal entoderm, 

 in which area the pharyngeal epithelium shows a distinct reaction 

 evinced by an increased thickness of its cells. This area of contact 

 ... is found at the end of the ventral flexure of the notochord as this 

 bends ventrally to pass from the vertebral anlagen to the retro- 

 pharyngeal region. . . 



This area is separated from the region of Eathke's pouch and 

 Seessel's pocket by practically the whole length of the future pha- 

 ryngeal vault." 



The condition in my own Ferret embryo is as follows. The embryo 



