ANATOMY OF A 17.8 MM. HUMAN EMBRYO 59 



glossopharyngeal. The glossopharjnigeal nerve, having passed on 

 the cephalic aspect of the ganglion nodosum, leaves the vagus, 

 but gives to it a communicating branch (also omitted from the 

 reconstruction) which contributes fibers to the pharyngeal 

 branch of the vagus. The glossopharyngeal then extends medi- 

 ally, bifurcating into a lateral or pharyngeal branch and a medial 

 or lingual branch. The pharyngeal branch (plate 6) sends a 

 twig to the developing stylo-pharyngeus muscle, and continues 

 cephalad, for a short distance, along the pharynx. The lingual 

 branch which is somewhat larger than the pharyngeal, also gives 

 off a small branch to the pharynx, and then passes in a cephalo- 

 medial direction to the lateral -side of the caudal part of the 

 tongue where it splits up into many branches. 



The glossopharyngeal trunk which extends peripherally from 

 the ganglion nodosum, is usually considered as the posttrematic 

 ramus of the second branchial cleft. 



A'', vagus. The vagus (N.vag., plates 2, 3 and 6) is a large, 

 mixed nerve, its main sensory component being derived from two 

 ganglia, the jugular {G.jug.) and the nodosum {G.nodos.). The 

 vagus acquires additional sensory fibers from an irregular series 

 or chain of ganglionic masses (Gg.hyp.) situated caudad of the 

 jugular ganglion and dorsal to the accessory nerve {N.acc). 

 These irregular clumps of cells without doubt represent hypo- 

 glossal ganglia, but the exact number of ganglia formed by them 

 is uncertain. Prentiss ('11) in dissected pig embryos frequently 

 found fibers from two or three of such ganglia passing ventrally 

 to join the corresponding motor roots of the hypoglossal nerve. 

 Such fibers, however, were not found in this embryo. The chain 

 of ganglia (Gg.hyp.) on the left side (plate 2) is continuous with 

 the first cervical ganglion which is very slender in its middle 

 part. 



Small motor rootlets issuing from the myelencephalon ventral 

 to the entering sensory fibers, together with fibers from the ac- 

 cessory, furnish the motor components of the vagus. The vagus, 

 therefore, from its sensory as well as from its motor composition, 

 is a compound nerve, as has been maintained by many investi- 

 gators. 



