DEVELOPMENT OF THE ALIMENTARY TUBE AND APPENDED ORGANS. 329 



socalled intermediate tubules, the cells changing to a flat type. The high 

 columnar cells of the terminal tubules become the serous secreting cells. 



Quite similar changes also occur in the submaxillary, but in foetuses of 

 eight to nine months the crescents of Gianuzzi appear as masses of darkly 

 staining cells forming the ends or sides of the terminal tubules. The crescents 

 at first border on the lumina, but later, probably by a process of evagination, 

 come to lie on the surface of the tubules. 



The beginning of the secretory function may be detected by a diminution in 

 the affinity of the cells for stains. 



The Pharynx. 



The pharynx develops from the cephalic end of the primitive gut. This 

 part of the gut is primarily of uniform diameter, is broadly attached by meso- 

 derm to the dorsal body wall, and ends blindly (Fig. 285). When the branchial 

 arches and grooves develoo in this (the cervical) region, they affect the gut as 



Neural tube 

 (brain) 



Maxillary process 

 Mandibular process 



Heart -- . 



, Notochord 



. Branchial arches and 

 grooves (pharynx) 



;-- Lung groove 



FIG. 294. Sagittal section through the head of a human embryo of 4.2 mm. (31-34 days). His. 



well as the periphery of the body. The arches form ridges on the surface of the 

 body (Fig. 122) and at the same time form ridges on the wall of the gut. The 

 grooves form pockets which alternate with the arches (Fig. 294). The pockets 

 in the pharyngeal cavity, or inner branchial grooves, are directed outward 

 toward corresponding outer branchial grooves (Fig. 287). The arches are 

 covered externally with ectoderm, internally with entoderm, and are filled with 

 mesoderm. Between the arches, or in the grooves, the ectoderm and entoderm 

 are in contact or nearly so. Thus the pharynx is not surrounded by a ccelomic 

 cavity. 



