3 90 A NA TOMICA L TECHNOL OGT. 



In tracing the vagus, be very careful to preserve all the branches 

 either given off or received by it. The main nerve is so large that 

 there is little danger of injuring it, but its branches are often very 

 small. It is a great help to pull the nerve in various directions with 

 the fingers or forceps ; then the presence of branches or anasto- 

 moses may be detected by the tense lines extending from the main 

 nerve. There are several of these branches which leave or join the 

 nerve on its way from the 1st rib to the aorta. One or two of these 

 come from the thyroid ganglion, two or three from the vertebral 

 ganglion. When near the arch of the aorta, the ventral side of the 

 vagus is crossed by the lesser cardiac nerve on its way to the car- 

 diac plexus from the vertebral ganglion (Fig. 107, N. crd.). 



1038. N. laryngeus recurrens s. inferior (Fig. 107, 108). 

 Just before crossing the ventral side of the aorta, the left vagus gives 

 off a large branch, which winds around to the dorsal side of the aorta 

 and follows the trachea cephalad to the larynx. Its origin may be 

 readily determined ; but to trace it on the trachea, the vessels should 

 be carefully removed in order to expose the trachea. This should 

 be deferred, however, until the vagus is traced to the stomach, or 

 it should be traced upon another specimen. 



1039. The vagus gives many branches to the heart and lungs 

 near the point where the nerve crosses the arch of the aorta. Their 

 branches are usually rather small, but their course may be made 

 out by pulling on the main nerve. 



In tracing the vagus caudad of the arch of the aorta, the lung 

 should be turned mesad, so that the nerve may be seen as it passes 

 along the dorsal side of its root (Fig. 107). In following the nerve 

 in the remainder of its course, it is especially desirable to draw it 

 tense, for in this way is most surely and easily determined the pres- 

 ence of branches. Just caudad of the root of the lung, the nerve 

 will be found to divide, one part passing along the dorsal aspect of 

 the oesophagus, and the other remaining on its ventral surface. 



1040. Follow the ventral branch (N. gastricus ventralis, Fig. 

 103, 107). About half way between the root of the lung and the 

 diaphragm, there will be seen a branch joining it from the right. 

 This can be seen easily by pulling the nerve cephalad and to the 

 left. This branch is the ventral division of the riglit vagus. The 

 combined trunks now pass along the diaphragm and penetrate it 

 with the oesophagus. The diaphragm may be cut away, and then 



