THE VAGUS NERVE. 387 



cliium to a point somewhat distad of its middle. Here it divides 

 into two divisions a dorsal, which winds around to the dorsal side 

 of the manus, a neutral, which extends along the ventral surface to 

 the palm. Near the distal third of the antebrachium the ventral 

 division sends a considerable branch to the group of tactile hairs 

 near the hypothenar eminence (Fig. 105). If the skin is torn from 

 the antebrachium at this point, the roots of the hairs will be seen 

 to be similar to those of the vibrissse (Fig. 87, 88). In distribution 

 the ulnar is partly cutaneous, but chiefly muscular. 



Dissection. The dissection of the ulnar nerve is very simple, 

 and needs no special directions. 



1029. N. thoracicus posterior The external respiratory nerve 

 of Bell (Fig. 104, 105, 106 ; Quain, A, I, 576 ; Gray, A, 671). The 

 long thoracic or external respiratory nerve (so called because the 

 phrenic was called internal respiratory) arises wholly from the 7th 

 cervical near its roots. It passes nearly caudad to be distributed 

 to the serratus magnus muscle. It may be seen readily as shown 

 in Fig. 105. 



Dissection. The rhomboideus and trapezius muscles should be 

 divided and the vertebral border of the scapula turned laterad. 

 The nerve may then be easily traced from its distribution to its 

 origin. 



NERVUS VAGUS, s. PAR VAGUM, . N. PNEUMOGASTRICUS, 10TH PAIR. 

 (Fig. 101, 105, 107 ; PI. II, Fig. 3, N. v. [x]). 



References. Quain, A, I, 557 ; Gray, A, 660 ; Hyrtl, A, 521 ; Gegenbaur (Lankester), 

 A, 518 ; Chauveau, A, 772 ; Chauveau (Fleming), A, 728 ; Gurlt, A, 737 ; Owen, A, III, 

 159 ; Milne-Edwards, A, II, 340 ; Leyh, A, 526 ; Dalton, A, Fig. 482 ; Stowell, 1. 



1030. The vagus or pneumogastric nerve (x) arises apparently from the side of the 

 medulla, passes laterad and traverses the Fm. jugulare in connection with the glossopha- 

 ryngeus and accessorius. Just as it emerges from the skull or just within the foramen, 

 it has a ganglion, the ganglion of the root, and about 1-2 cm. farther peripherad it pre- 

 sents a second ganglion, the ganglion of the trunk. The nerve passes along the neck in 

 company with the carotid artery, and from the ganglion of the trunk to a point near the 

 1st rib is so closely connected with the sympathic nerve that the two appear like one (Fig. 

 107). The vagus enters the thorax mesad of the A. sternnlis, extends caudad along the 

 ventral aspect of the A. subdavia sinistra ( 930), crosses the arcus aorticus, and while 

 crossing it gives off a long branch, the N. laryngeus recurrens, which winds around the 

 arch and extends cephalad along the trachea to the larynx (Fig. 107). The vagus then 

 passes caudad along the dorsal side of the root of the lung. Slightly caudad of the root 

 of the lung it divides into two parts ; one, extending along the ventral side of the O3sopha- 

 gus, soon unites with a branch from the right vagus (Stowell, T), and the combined trunk, 

 the ventral gastric nerve, then passes along the oesophagus, penetrates the diaphragm and 



