PHARYNX AND TONGUE 



159 



the whole forming a forked elevation called by His the furcula (fig. 200). In 

 front of the furcula a rounded swelling is developed in the angular space between 

 the ventral ends of the first and second arches named the tuberculum impar (His). 

 Development of the tongue, It is on the flat floor of the pharynx thus 

 defined that the tongue takes form. According to His' account, the tuberculum 

 impar enlarges, projects forward on the oral surface of the mandibular arch, and 

 forms the body of the organ. It appears, however, from the extensive comparative 



FIG. 201. SIMILAR VIEWS IN OLDER EMBRYOS OP THE SAME PARTS AS IN FIG. 200. (His.) A, 



T, tuberculum impar. 



; 3, 



researches of Kallius, confirmed in the ease of the human embryo by Hammar, 1 

 that the greater part of the body of the tongue is really formed, as Born, indeed, 

 showed for the pig in 1883, from two lateral swellings which rise from the floor of 

 the mouth and surround the tuberculum impar. According to Hammar, the tuber- 

 culum impar forms' in the human tongue only a small portion in front of the 

 foramen caecum, but Kallius holds that it gives rise to the central part of the 

 organ. The lateral tongue-ridges are marked off externally by grooves which 

 deepen, as development proceeds, into 

 the alveolo -lingual sulci. The root of 

 the organ is formed from a transverse 

 ridge which develops between the ventral 

 ends of the second arches (Born, 

 Hammar). From this ridge two swellings 

 grow forwards to embrace, as with the 

 limbs of a V, the tuberculum impar 

 (fig. 201). At the apex of the V, and 

 between its limbs, a deep recess marks 

 the rudiment of the mesial thyroid. The 

 line of union between this (copular) part 

 of the tongue and the body is marked in 

 the adult by the sulcus terminalis of His, 

 and the depression is represented by the 



foramen ccecum (fig. 202). The root of the tongue is at first continuous with the 

 ridge which lies between the ends of the third arches and in front of the 

 primitive glottis. Later a fold develops on this ridge, which is the rudiment of 

 the epiglottis. 



FIG. 202. SIMILAR VIEW IN A CONSIDERABLY 

 OLDER EMBRYO, BUT LESS MAGNIFIED. 

 (His.) 



1 See Hammar, Arch. f. mikr. Anat. Ixi. 102; C. Rabl, Die Entwickelung des Gesichtes, Heft i. 

 1 ( JU2; Kallius, Anat. Anzeiger (Ergiinzungsheft), xxiii. 1903. 



