398 



ELEMENTARY ANATOMY. 



[LESS. 



the mucous membrane of the tongue and pharynx and seme 

 of the muscles of those parts. Its essential nature is revealed 

 by lower forms, where (as e.g. in the Shark Hexanchus] it 

 bifurcates (Fig. 349, ", hy, and 2 ), and sends one branch to the 

 posterior margin of the hyoidean arch, and another along 

 the anterior margin of the first branchial arch. This fact 

 may explain its pharyngeal distribution in man. 



The second, called the pneumo-gastric, or nervus vagtis, 

 is the longest of all the cranial nerves, as it supplies not 

 only the organs of the voice and of respiration, but also the 



FIG. 350. INFERO-LATERAL VIEW OF HEAD AND AORTIC ARCHES OF 



LEPIDOSIKEN. 



a, oesophagus ; b, anterior end of bulbus aortse ; c, common roots of the first 

 aortic arches ; d, third aortic arch; e, first aortic arch \f, dorsal union of the 

 first three aortic arches ; g~, aorta ; //, cceliac artery ; z, exit of the fifth nerve ; 

 k, part of operculum ; /, exit of the nervus vagus from the skull ; m, branches 

 to oesophagus ; n, nerve going to the rectus abdominis ; o, nervus lateralis ; 

 /, _first and hypertrophied rib : g, posterior part of skull ; r, segmented neural 

 spines ; s, chorda dorsalis ; /, mandible ; ?, quadrate. 

 (After Hyrtl.) 



heart and the stomach. It sends back two branches to the 

 larynx, which are called " re-current," and the relations of 

 which to the arterial trunks are different on the two sides 

 of the body. The essential nature of this nerve is revealed 

 by the lowest Vertebrates, where (as in Fishes) we find it 

 made up of a great trunk, arising by many rootlets from the 



