40 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



pharynx in front (Fig. 30), is covered by glandular and lymphoid 

 tissue and concerned with swallowing. 



The buccal part arises during the 3rd week from the mandibular 

 or 1st arch and the 1st interbranchia'l space by the upgrowth of a 



Phar 

 part 



2nd and 3rd- 



a re lies T'-.-A 



Fig. 30.— Showing the Buccal and Pharyngeal parts of the Tongue. 



tubercle, the tuberculum impar (Fig. 31). Being mandibular in 

 origin, it is supplied by the mandibular nerve (3rd div. of Vth), 

 and its main attachment is to the mandible. Although its 

 bilateral origin is not apparent during development, the lingual 

 septum, the occasional occurrence of cysts in the middle line and 

 its bifid condition in lower vertebrates and occasionally in man, 

 make it extremely probable that it derives a half from each side 

 of the mandibular arch. 



The pharyngeal part of the tongue is derived from the fused 

 ventral ends of the 2nd and 3rd arches in which, as we have 

 already seen, the body of the hyoid is developed. The glosso- 

 pharyngeal, the nerve of the 3rd arch, or more strictly of the 2nd 

 cleft, supplies it. The V-shaped groove (sulcus terminalis) marks 

 the union of the tuberculum impar with the basal or pharyngeal 

 part. From the hypoblast, which lines the depression between 

 those two parts, arises, by a process of outbudding, the middle 

 lobe or isthmus of the thyroid gland (Fig. 34). 



