34 



HUMAN EMBRYOLOGY AND MORPHOLOGY. 



arches come to form the bone of the tongue. The skeletal part 

 of the hyoid arch suspends the tongue. 



The great horn of the hyoid represents the cartilage of the 

 3rd arch (Fig. 26). The formation of the larynx and lungs from 



incus 



malleus 



tympanic 

 tympano-hyal. 



stylo-hyal. 



arch— Meckel's cart. 



arch — stylo-hyoid 

 thyro-hyoid 



4th arch 

 5th arch 



Fig. 26.— Showing what hecome of the Cartilages of the Visceral Arches. 



the ventral part (floor) of the pharynx renders it difficult to say 

 what becomes of the cartilage of the 4th arch, but it probably 

 forms the whole or part of the thyroid cartilage. The thyroid in 

 Marsupials is composed of an upper and lower segment, hence it 

 is supposed that it may represent both the cartilages of the 

 4th and 5th arches. A perforation for vessels near the middle 

 of the thyroid cartilage, on each side, sometimes occurs in 

 man. 



The Nerves of the Visceral Arches. — The 3rd division of the 

 Vth nerve is, as has been already seen, the principal nerve of the 

 first or mandibular arch. The nerve for the second or hyoid arch is 

 represented by the 7 th and 8 th (facial and auditory, Fig. 27). 

 The nerve of the 3rd arch is the glosso-pharyngeal, that for 

 the 4th is the superior laryngeal branch of the vagus, and for 

 the 5th the inferior laryngeal (Fig. 27). 



Each nerve of a visceral arch, however, sends a branch to the 



