268 CONSTRICTOR AND DILATOR FIBRES. [BOOK i. 



sympathetic are enclosed in a common sheath so as to form what 

 appears to be a single trunk), which reach the gland in company 

 with the arteries supplying the gland (n, sym. sm.). On the 

 other hand it receives fibres from a small nerve called the chorda 

 tympani (ch. t.), which, springing from the 7th cranial (facial) 

 nerve, crosses the tympanum of the ear (hence the name), and, 

 joining the lingual branch of the 5th nerve, runs for some distance 

 in company with that nerve, and then ends partly in the tongue, 

 and partly in a small nerve which, leaving the lingual nerve before 

 reaching the tongue, runs along the duct of the submaxillary 

 gland, and is lost in the substance of the gland ; a small branch 

 is also given off to the sublingual gland. 



Now, when the chorda tympani is simply divided, no very 

 remarkable changes take place in the blood vessels of the gland, 

 but if the peripheral segment of the divided nerve, that still in 

 connection with the gland, be stimulated, very marked results 

 follow. The small arteries of the gland become very much dilated, 

 and the whole gland becomes flushed. (As we shall see later on 

 the gland at the same time secretes saliva copiously, but this does 

 not concern us just now.) Changes in the calibre of the blood 

 vessels are, of course, not so readily seen in a compact gland as in 

 a thin extended ear ; but if a fine tube be placed in one of the 

 small veins by which the blood returns from the gland, the effects 

 on the blood flow of stimulating the chorda tympani become 

 very obvious. Before stimulation the blood trickles out in a thin, 

 slow stream of a dark venous colour ; during stimulation the blood 

 rushes out in a rapid full stream, often with a distinct pulsation, 

 and frequently of a colour which is still scarlet and arterial in 

 spite of the blood having traversed the capillaries of the gland ; 

 the blood rushes so rapidly through the widened blood vessels that 

 it has not time to undergo completely that change from arterial to 

 venous which normally occurs while the blood is traversing the 

 capillaries of the gland. This state of things may continue for 

 some time after the stimulation has ceased, but before long the 

 flow from the veins slackens, the issuing blood becomes darker 

 and venous, and eventually the circulation becomes normal. 



We shall have occasion later on to speak of the nervi erigentes, 

 the stimulation of which gives rise to the erection of the penis. The 

 erection of the penis is partly due to a widening of the arteries 

 supplying the peculiar erectile tissue of that organ, whereby that 

 tissue becomes distended with blood, and the widening is brought 

 about by impulses passing along the nerves in question. Obviously 

 the chorda tympani and the nervi erigentes contain fibres which 

 we may speak of as ' vaso-motor ' since stimulation of them 

 produces a change in, brings about a movement in the blood 

 vessels ; but the change produced is of a character the very 

 opposite to that produced in the blood vessels of the ear by 

 stimulation of the cervical sympathetic. There stimulation of the 



