846 



DEVELOPMENT 



[CH. LIX 



anterior part of the head which is called the fronto-nasal process. The 

 back of the space is bounded for a time by a thin membrane which 

 separates the foregut from the stomadaeum. Just in front of the 

 upper end of this membrane a diverticulum projects from the 

 stomadseum towards the brain this is Kathke's 

 pouch ; it meets a downgrowth from the brain 

 called the hypophysis, and the two structures 

 unite to form the two lobes of the pituitary 

 body. The membrane soon disappears, and the 

 primitive mouth and the foregut form a con- 

 tinuous cavity. In the meantime two olfactory 

 FIG. 64o.-Diagram representing pits have appeared on the under surface of 

 a ron ver v y ie you f ng nt embryo arb i, ? he fronto-nasal process, and they grow back 

 Fronto-nasai process of head ; into the roof of the stomadseum. These pits 



2, (olfactory pit; 3, stoma- 



daeum ; 4, umbilical orifice ; 5, cut the fronto-nasal process into three parts, 



a1cl7?, iu eye ; . 6> E r the mesial nasal process between them, and the 



lateral nasal processes at the sides. Moreover, 



two little projections, the globular processes, grow down on each side of 

 the middle line from the mesial nasal process. At this period the 



FIG. 641. Diagram of anterior 

 view of an embryo older than 

 that shown in fig. 640. 1, 

 Mid-brain ; 2, fore-brain ; 3, 

 eye ; 4, olfactory pit ; 5, 

 stomadreum; 6, pericardium; 

 7, umbilical orifice ; 8, third 

 visceral arch ; 9, second 

 visceral arch ; 10, first or 

 mandibular arch ; 11, max- 

 illary process of mandibular 

 arch ; 12, globular process ; 

 13, mesial nasal process ; 14, 

 lateral nasal process. 



FIG. 642. Diagram representing a 

 later stage of development of the 

 face than that shown in fig. 641. 

 1, Mid-brain ; 2, fore-brain ; 3, eye ; 

 4, anterior nasal orifice ; 5, globular 

 process ; 6, mouth ; 7, pericardium; 

 8, second visceral arch ; 9, first 

 visceral arch ; 10, maxillary pro- 

 cess of first arch ; 11, lateral nasal 

 process. 



upper boundary of the orifice of the stomadseum is formed by the 

 two globular processes separated by a small cleft, and the two lateral 

 nasal processes saparated from the globular processes by the olfactory 



