60 F. W. THYNG 



Each vagus nerve extends caudad upon the medial side of the 

 internal jugular vein as far as the common cardinal vein. It then 

 occupies the angle between the oesophagus and trachea until the 

 latter bifurcates. From here each nerve, as it continues caudad, 

 passes dorsally to the bronchus of its own side where it gives off 

 pulmonary branches. More caudally the nerves are in close 

 relation to the oesophagus, forming a coarse plexus superficial 

 to the anlage of the external muscular layer. From the oesopha- 

 gus the vagi spread onto the stomach and give branches to the 

 neighboring viscera. 



An auricular branch of the vagus has not been identified on 

 either side of this embryo. It is possibly a nerve of late develop- 

 ment. In rare instances its absence has been noted in the adult. 



A short, rather ill-defined pharyrgeal branch is present on 

 either side (but not reconstructed). Each arises irom the medial 

 side of the cephalic part of the ganglion nodosum, and extends to 

 the pharynx, passing ventral to the proximal part of the internal 

 carotid artery. -To the formation of this nerve on either side the 

 glossopharyngeal seems to contribute fibers as mentioned above. 

 These branches of the vagus are apparently late in becoming 

 formed into definite trunks. 



The superior laryngeal nerve {N.Ls., pi. 3; N.laryng.s., 

 pi. 6) arises at the ganglion nodosum, slightly caudad of its 

 middle. It is represented in plate 3 as a stump, but is shown in 

 part in plate 6. It extends ventrally and medially, dorsal to 

 the distal part of the common carotid artery, and caudad of the 

 detached (from pharynx) end of the thymico-pharyngeal duct, 

 to divide into two branches, internal and external. 



The internal branch passes medially over the cephalic border 

 of the lateral lamina of the thyreoid cartilage, and divides into 

 dorsal and ventral branches. The dorsal extends in the mesen- 

 chyma between the entodermal portions of the oesophagus and 

 larynx. The ventral extends caudad, medial to the lateral lamina 

 of the thyreoid cartilage. The external branch of the superior 

 laryngeal is smaller than the internal, and can be traced caudally 

 along the lateral aspect of the thyreoid cartilage for a short 

 distance. 



