i6o 



THE DISSECTION OF PIG EMBRYOS FOR STUDY 



the union of the second branchial arches forms the copula. This, with the por- 

 tions of the second arches lateral to it, forms later the base or root of the tongue. 

 Between it and the tuberculum impar is the point of evagination of the median 

 thyreoid gland. The copula also connects the tuberculum impar with a rounded 

 prominence which is developed in the mid- ventral line from the bases of the third 

 and fourth branchial arches. This is the anlage of the epiglottis. In later stages 

 (Fig. 151 A and B) the lateral mandibular anlages increase rapidly in size, are 

 bounded laterally by the linguo-alveolar grooves, and fuse with the tuberculum 

 impar which lags behind in development and is said to form the median septum 

 of the tongue. According to Hammar, it completely atrophies. The epiglottis 

 becomes larger and concave on its ventral surface. Caudal to it, and in early 



Lateral t&ngue Thyreoid 

 diverticulum 



Lateral tongue swellings 



Entrance to 

 larynx 



Entrance to 



larynx 

 Arytenoid 

 swellings 



FIG. 152. The development of the tongue in human embryos. A, 5 mm.; B, 7 mm. (modified from 



Peters). 



stages continuous with it, are two thick rounded folds, the arytenoid folds. Be- 

 tween these is the slit-like glottis leading into the larynx (see p. 174). 



The musculature of the tongue is supplied chiefly by the hypoglossal nerve, and both nerve 

 and muscles develop caudal to the branchial region in which the tongue develops. The mus- 

 culature migrates cephalad and gradually invades the branchial region beneath the mucous 

 membrane. At the same time, the tongue may be said to extend caudad until its root is cov- 

 ered by the epithelium of the third and fourth branchial arches. This is shown by the fact 

 that the sensory portions of the nn. trigeminus and facialis, the nerves of the first and second 

 arches, supply the body of the tongue, while the nn. glossopharyngeus and vagus, the nerves of 

 the third and fourth arches, supply the root and the caudal portion of the body of the tongue. 



In embryos of 50 to 60 mm. the fungiform and filiform papillae may be dis- 

 tinguished as elevations of the epithelium. Taste buds appear in the fungiform 

 papillae of 100 mm. embryos and are much more numerous in the fetus than in 

 the adult. The vallate papilla (Fig. 153 A) appear at 90 mm. as a V-shaped epi- 



