DEVELOPMENT OF THE ALIMENTARY TUBE AND APPENDED ORGANS. 321 



part of the nasal cavity from the pharynx. Thus the posterior nares and 

 pharynx are left in communication. Externally the maxillary processes extend 

 medially, separate the nasal pits from the oral cavity, and form the lateral 

 portions of the upper lip (Fig. 137). 



Jacobson's organ 

 Inferior concha 



Jacobson's cartilage 



Palatine process 



Nasal septum 



Nasal cavity 



Oral cavity 



FIG. 286. From a section through the head of a human embryo of 28 mm., showing the nasal 

 septum, the nasal cavities, the oral cavity, and the palatine processes. Peter. 



The Tongue. The tongue develops from three separate anlagen which 

 unite secondarily. In embryos of about 3 mm. a slight elevation appears on the 

 floor of the pharynx in the region of the first branchial arch. This is the 



Tuberculum impar 



Mandibular 

 process 



Root of tongue 



Inner branchial 

 groove IV 



Crista terminalis 



Lung 

 FIG. 287. Floor of the pharyngeal region of a human embryo of about 3 weeks. His. 



tuberculum impar, being, as the name indicates, unpaired, and is destined to give 

 rise to the tip and body of the tongue (Fig. 287) . Soon afterward two bilaterally 

 symmetrical elevations appear on the floor of the pharynx, which are destined to 

 give rise to the root of the tongue (Fig. 288). These paired elevations, arising 



