Johnston, Forehrain Vesicle in Vertebrates. 



475 



and anterior head cavities are small, sejDarate from each other, but 

 both connected with the median mass which is crowded behind the 

 "infundibnlnm." The median band connecting- the anterior cavities 



a.h.c 

 pr.m j 





e.n. 



md 



Fig. 11. Squalus ac, 30 somites, frontal section through premandibular and 

 anterior head cavities, x 150. 



is small and disappears at this stage. The premandibular somites 

 retain the connection with the median mass in which cavities appear 

 in later stages and finally fuse with the cavities of the premandib- 

 ular somites as fully described by l^eal and others. The anterior 



