COURSE OF THE VASO-DILATOR NERVES. 679 



the blood-vessels of the penis ( 362, 4) ; but if their peripheral ends be stimulated 

 with Faradic electricity, the sinuses of the corpora cavernosa dilate, become filled 

 with blood, and erection takes place ( 436). Other examples in muscle and else- 

 where are referred to below.] 



Course of the Vaso-dilator Nerves. To some organs they pass as special nerves to other 

 parts of the body, however, they proceed along with the vaso-motor and other nerves. Accord- 

 ing to Dastre and Morat, the vaso-dilator nerves for the bucco-labial region (dog) pass out from 

 the cord by the 1st to the 3rd dorsal nerves, and go through the rami communicantes into the 

 sympathetic, then to the superior cervical ganglion, and lastly through the carotid and inter- 

 carotid plexus into the trigeminus. [The fibres occur in the posterior segment of the ring of 

 Vieussens, and if they be^stimulated there is dilatation of the vessels in the lip and cheek on 

 that side (p. 624).] The maxillary branch of the trigeminus, however, also contains vaso- 

 dilator fibres proper to itself (Laffont). In the grey matter of the cord, there is a special 

 subordinate centre for the vaso-dilator fibres of the bucco-labial region. This centre may be 

 acted on reflexly by stimulation of the vagus, especially its pulmonary branches, and even by 

 stimulating the sciatic nerve. The ear receives its nerves from the 1st dorsal and lowest cervical 

 ganglion, the upper limb from the thoracic portion, and the lower limb from the abdominal 

 portion of the sympathetic. The vaso-dilator fibres run to the sub-maxillary and sub-lingual 

 glands in the chorda tympani ( 349, 4), while those for the posterior part of the tongue run 

 in the glosso-pharyngeal nerve ( 351, 4 Vulpian). Perhaps the vagus contains those for the 

 kidneys ( 276). Stimulation of the nervi erigentes proceeding from the sacral plexus causes 

 dilatation of the arteries of the penis, together with congestion of the corpora cavernosa ( 436) 

 (Eckhard, Loven). Eckhard found that erection of the penis can be produced by stimulation of 

 the spinal cord and of the pons as far as the peduncles, which may explain the phenomenon of 

 priapism in connection with pathological irritations in these regions. The muscles receive 

 the vaso-dilator fibres for their vessels through the trunks of the motor nerves. Stimulation 

 of a motor nerve or the spinal cord causes not only contraction of the corresponding muscles, 

 but also dilatation of their blood-vessels ( 294, II. 0. Ludwig and Sczelkow, Hafiz, Gaskell) 

 the dilatation of the vessels taking place even when the muscle is prevented from shortening. 

 [Gaskell observed under the microscope, the dilatation produced by stimulation of the nerve to 

 the mylohyoid muscle of the frog.] The vaso-dilators remain medullated up to their terminal 

 ganglion {Gaskell). 



The vaso-dilators (like the vaso-motors, p. 676) also have subordinate 

 centres in the spinal cord; e.g., the fibres of the labio-buccal region at the 

 1st to 3rd dorsal vertebrae. This centre may be influenced reflexly through the 

 pulmonary fibres of the vagus, and also through the sciatic {Laffont, Smirnow). 

 According to Holtz, a similar centre lies in the lowest part of the cord. 



Goltz showed that, in the nerves to the limbs (e.g., in the sciatic nerve), the vaso-motor 

 and vaso-dilator fibres lie side by side in the same nerve. If the peripheral end of this nerve 

 be stimulated immediately after it is divided, the action of the vaso-constrictor fibres overcomes 

 that of the dilators. If the peripheral end be stimulated 4 to 6 days after the section, when the 

 vaso-constrictors have lost their excitability, the blood-vessels dilate under the action of the 

 vaso-dilator fibres. Stimuli, which are applied at long intervals to the nerve, act especially on 

 the vaso-dilator fibres ; ivhile tetanising stimuli act on the vaso-motors. The latent period of 

 the vaso-dilators is longer, and they are more easily exhausted than the vaso-motors (Bowditch and 

 Warren). The sciatic nerve receives both kinds of fibres from the sympathetic. It is assumed 

 that the peripheral nervous mechanisms in connection with the blood-vessels are influenced by 

 both kinds of vascular nerves ; the vaso-motors (constrictors) increase, while the vaso-dilators 

 diminish the activity of these mechanisms or ganglia. [It is, however, possible to explain their 

 effects by supposing that they act directly upon the muscular fibres of the blood-vessels, without 

 the intervention of any nervous ganglionic structures.] 



[Section of the spinal cord high up in the neck causes, of course, a great fall of the blood- 

 pressure, owing to the division of the vaso-motor nerves. In the dog the pressure may fall 

 to 30-40 mm. Hg. After isolation of the cord, in rabbits alone, stimulation of the central 

 end of a sensory nerve causes a rise of the blood-pressure ; in dogs, however, under the same 

 conditions, the blood-pressure falls. Dyspuceic blood also causes a rise of the blood-pressure, 

 which is preceded by a fall (Ustimowitch). This reflex fall of the blood-pressure takes place 

 after section of the splanchnics, and the nerves to the extremities, but it does not take place if 

 the spinal cord be divided at the lumbar or lower dorsal region. If the cord be divided in the 

 lower dorsal region, stimulation of the brachial plexus has no effect, while the fall occurs after 

 stimulation of the central end of the sciatic. These experiments indicate that the vaso-dilator 

 nerves which cause the fall of the blood-pressure arise in the lower part of the spinal cord 

 (lumbar), and that they are probably contained in the visceral nerves and not in those for the 

 extremities (Thayer and Pal).] 



