358 



B. F. KINGSBURY 



remains closely joined to the third pouch so that as long as it 

 persists, it is a component of the head of the Complex III. 

 My observations, however, confirm those of previous investi- 

 gators that in man it contributes nothing to the pharyngeal 

 derivatives, whereas in some mammals it unquestionably under- 



Fig. 9 Lateral (surface) view of the ectodermal pharyngeal surface, in a 

 7.5mm. human embryo (No. 256, Harvard Embryological Collection), as modelled 

 with the entoderm (shown in figures 13 and 14). 



Fig. 10 Surface (lateral) view of the branchial arches and clefts in a 9.4 

 mm. human embrj-^o, as shown in a model, the posterior aspect of which is given 

 in figure 19. 



Fig. 11 Surface view, from the left side, of the branchial region in a 10 mm. 

 human embryo (No. 1000, Harvard Embryological Collection), from a model 

 of the ectoderm. Other aspects of the model are shown in figures 15, 16 and 17 

 S.C., indicates the external portion of the cervical sinus (sulcus cervicalis). 



goes thymic transformation, as will be commented on sub- 

 sequently. Its position and relations in the Complex III are 

 shown in figures 20, 21 and 22. 



The external portion of the cervical sinus owes its existence 

 more to the growth of the postbranchial territory, together with 



