DEVELOPMENT OF THE PHARYNX AND NECK. 



41 



The Musculature of the Tongue.— The muscles of the tongue 

 do not arise within the visceral arches, but are of extraneous 

 origin. It will be shown subsequently that the head is probably 

 composed of nine segments, and it is from the muscle plates of the 



buccal part 



Nerve of 1st arch' 

 (3rddiu. of 5th) 



ceruic. sinus. 



-1st arch 



ft— 2nd arch 

 pharyng. part. 



epiglottis 

 foramen caecum 



3rd arch 

 4th arch 



FIG. 31. — Showing the origin of the tongue in the floor of the primitive pharynx. 

 The condition reprjsented is from an embryo in the 6th week. (After His.) 



posterior four or five of these segments that the tongue muscles 

 are derived. Processes from the muscle plates of these segments 

 grow downwards and forwards until they reach the basis of the 

 tongue derived from the three visceral arches, carrying their nerves 

 with them — the hypoglossal or 12th cranial nerve, which contains 

 the motor nerve fibres of the posterior segments of the head. 

 Hence, while the sensory nerves of the tongue come from the 

 nerves of the, 1st, 2nd and 3rd visceral arches, its motor fibres 

 are derived from the posterior cephalic segments. 



Lingual Papillae. — The filiform papillae are the first to appear, 

 then the fungiform, a few of which, along the posterior border of 

 the buccal part, become enlarged and sink to form circumvallate 

 papillae, round the bases of which taste buds are developed. The 

 papillae are confined to the buccal or masticatory part of the 

 tongue. It will be observed that the taste papillae are situated 

 at the brink of the pharnyx (Fig. 30), at which the food is seized 

 and carried away by the involuntary muscles. At the lateral 

 margins of the buccal part of the tongue, just in front of the 

 anterior pillars of the fauces, the fungiform papillae are arranged 



