3 86 COMPARATIVE ZOOLOGY OF CHORD ATES 



In the lateral and collateral sympathetic ganglia are the 

 cell-bodies of the postganglionic or exciter neurons. These 

 run out of the ganglia as non-medullated and therefore grey 

 fibres, to the muscles of the blood-vessels, heart, stomach, 

 intestine, oviduct, bladder, and skin ; and some of them run 

 to the ciliary and iris muscles inside the eye. 



The effect of stimulation through the sympathetic system 

 is to slacken the ordinary muscles surrounding the gut, but to 

 tighten the sphincters, to tighten the heart and artery muscles, 

 to tighten the muscles under the skin (which make hair stand 

 " on end "), to tighten and slacken the muscles of the oviduct, 

 to slacken the sphincter and tighten the radial muscles of the 

 iris so that the pupil enlarges. 



The structures enumerated above are also innervated by the 

 parasympathetic system (except the muscles of the oviduct). 

 The visceral branch of the vagus contains connector fibres 

 which run to exciter neurons situated on the lungs, heart, and 

 the muscles of the gut as far as the end of the small intestine. 

 In the region of the intestine, the exciter neurons lie between 

 the muscle coats of the gut, forming the plexus of Auerbach. 

 The remainder of the gut is innervated by connector fibres 

 which leave the spinal cord in the sacral region through the 

 ventral nerve-roots, and form the pelvic nerve. These con- 

 nector fibres run to excitor neurons on the muscles of the large 

 intestine, on the bladder, on the skin round the anus, and on 

 the blood-vessels near the urethra. 



The ciliary and iris eye-muscles receive innervation by 

 means of connector fibres which run in the oculomotor nerve 

 to the ciliary ganglion. This ganglion contains the cell- 

 bodies of the exciter neurons which run to the muscles in 

 question in the eye. Two sets of autonomic connector fibres 

 run through the facial nerve. One goes down the palatine 

 branch (" greater superficial petrosal ") to the spheno-palatine 

 ganglion from which exciter neurons run to the lachrymal 

 glands and the glands of the nose. The other set runs 

 in the chorda tympani (ramus mandibularis internus facialis 

 of the dogfish) to the submaxillary ganglion, whence exciter 

 neurons run to the submaxillary salivary glands. Another set 



