THE MICROSCOPE. 67 



monary region, both on the sinistral and dorsal sides, the vagus 

 nerve divides into lateral and mesal rami (Fig. i, L. M.). The lat- 

 eral rami reunite a short distance cephalad of the diaphragm to 

 form a distinct nerve trunk, N. gastricus dorsalis, upon the dorsum 

 of the oesophagus in the caudal (posterior) mediastinum (Fig. i, 

 dor.); the mesal rami, taking a ventro-caudal course, unite slightly 

 cephalad of the union of the lateral rami, upon the venter of the 

 caudo-pulmonary oesophagus to form a ventral trunk, N. gastricus 

 ventralis (Fig. i, ven.). Caudad of the diaphragm these gastric 

 trunks supply the stomach, and terminal rami extend to the great 

 solar plexus. 



Such being the typical disposition of the two branches, it be- 

 comes desirable to establish the exact arrangement of the rami in 

 the rabbit. The prevailing plan in the rabbit in the dorso-pulmon- 

 ary region is as follows: The nerve trunks approach the ventri- 

 meson of the oesophagus until they lie apposed for 5-10 mm.; in this 

 relation N. vagus dexter divides and gives off a large mesal ramus 

 15-20 mm. in length which joins the sinistral trunk somewhat 

 caudad of the roots of the lungs (Fig. 2, M); the lateral ramus con- 

 tinues in a dorso-caudal direction and meets the sinistral trunk 

 upon the dorsum of the oesophagus about 55 mm. caudad. At this 

 point the nerves form two closely apposed trunks for about the 

 same distance as in the dorso-pulmonary region ; this arrangement 

 constitutes an oesophageal loop; in the dorso-oesophageal region the 

 sinistral nerve divides and sends a large mesal ramus to the lateral 

 ramus of the dextral nerve (Fig. 2, M). Caudad of the diaphragm 

 the disposition of the gastric nerves and terminal filaments presents 

 distinct characters, but too complex for this discussion. 



I have not called attention to the complex plexus formed by 

 oesophageal rami. In a rabbit recently studied, the dorso-pulmonary 

 portion of the ramus seemed to be a single trunk, and the dorso- 

 oesophageal portion instead of presenting the trunks in their apposed 

 relation, showed two distinct parallel trunks. Treatment with acid 

 and alcohol, under 25 diameters (confirmed by higher powers), re- 

 vealed a true chiasmus in which there is formed a crucial 

 interlacing of fibres (Fig. 3); the nerves of either side undergo a 

 characteristic decussation, — the lateral fibres continue caudad, the 

 mesal fibres decussate, sinistral becoming sinistral and dextral, and 

 dextral bec<jming dextral and sinistral; cephalic mesal fibres pass 



