THE STOMATODJEUM 



40 



Stomatodseum 



Globular process 



Olfactory pit 



Lateral 



nasal 



process 



Maxillary 



64. ANTERIOR VIEW OF BOUNDARIES OF 

 STOMATOD^UM BEFORE COMPLETION OF PRIMI- 

 TIVE UPPER LIP. 



The bucco-pharyngeal membrane disappears about the third week, and about 



the twenty-first day a diverticulum from the stomatodaeum is projected into the 



caudal surface of the head, from the point 



where that surface originally joined the 



dorsal end of the external surface of the 



bucco-pharyngeal membrane. The diver- 

 ticulum is Rathke's pouch. The cranial 



extremity of the pouch comes into relation 



with the hypophyseal diverticulum from 



the floor of the third ventricle, and dilates. 



The stalk which connects the dilated 



terminal part of the diverticulum with 



the stomatodseum disappears, and the 



terminal vesicle becomes the anterior lobe 



of the hypophysis (O.T. pituitary body) 



(Figs. 57, 62, 63). 



The Separation of the Stomatodseum 



into Nose and Mouth. In the cephalic FIQ 



boundary of the stomatodseal space lies 



the ventral end of the head, which is 



called the fronto-nasal process. 



In the fronto-nasal process, on each side of the median plane, is situated a 



shallow pit, the olfactory pit, and by the pits the process is divided into a median 



part, the median nasal process, and two lateral parts, the lateral nasal processes. 



Further, the margin of the median process is divided by a median cleft into 



right and left globular processes (Fig. 64). 



The orifices of the olfactory pits are directed laterally, therefore the lateral nasal 



processes lie dorsal to the median nasal process in the cranial boundary of the 



stomatodaeal space, and as their margins increase in height the pits deepen (Fig. 69). 

 At this period the cranial boundary of the stomatodaeum is divided by the 



median sulcus and the olfactory pits into four projections the two globular processes, 



each of which lies between the median 

 sulcus and an olfactory pit, and the 

 two lateral nasal processes, which form 

 the dorso-lateral borders of the olfactory 

 pits. The lateral boundaries are formed 

 by the maxillary processes and the dorsal 

 parts of the mandibular bars, and the 

 caudal boundary is formed by the medi- 

 ally turned and conjoined ventral parts 

 of the mandibular bars. Immediately 

 cranial to the maxillary process, on each 

 side, is the projecting eye ; and leading 

 from it, between the maxillary process 

 and the lateral nasal process, is the 

 naso-lacrimal sulcus. 



As growth proceeds and each maxil- 

 lary process grows ventrally, its ex- 



- Cerebral hemisphere 



-Lens 



Lateral nasal process 

 -Maxillary process 



-Mandibular arch 

 -Hyoid arch 

 -Third arch 



Pericardial region 



FIG. 65. SCHEMA OF ANTERIOR VIEW OF THE HEAD f rA t n jf v f 11<; p q w iP Aam nr 



OF A HUMAN EMBRYO SHOWING THE COMPLETION T 6mit S 6S 71 i faudal or P S - 



OF THE PRIMITIVE UPPER LTP. tenor border of the lateral nasal process, 



and then, carrying the lateral nasal 

 process with it, it fuses with the globular process of the same side. 



After the fusion of the maxillary processes, and the posterior or caudal 

 borders of the lateral nasal processes, with the globular processes has occurred/ 

 the olfactory pits are completely separated, for a time, from the stomatodseum, 

 and they lie in the ledge which now forms the cranial boundary of the stomato- 

 dseum. This ledge consists of the two globular processes, fused into a single mass, 

 and the two maxillary processes, the caudal or posterior l edges of the lateral nasal 



1 Inferior in erect posture. 



4 



