REPRODUCTION IN MAN 1229 



fibres, which pass out through the anterior roots of the third, fourth, and 

 fifth lumbar nerves (in the rabbit and cat), and run through the sympathetic 

 to the inferior mesenteric ganglia, whence they proceed by the hypogastric 

 nerves. On stimulating these fibres, two effects are produced on the uterus 

 and vagina, namely, a contraction of the small arteries, leading to pallor 

 of the organs, and a strong contraction of the muscular coats.* In the 

 vagina the contraction can usually be seen to start from one end and spread 

 to the other. The whole then remains for a time in a state of powerful 

 tonic contraction, which affects both longitudinal as well as circular muscles. 

 In the male stimulation of these nerves excites contraction of the whole 

 musculature of the vasa deferentia and seminal vesicles, which may be 

 strong enough to cause emission of semen from the penis. These effects on 

 the uterus and seminal vesicles are not abolished by injection of atropine. 



The course of the sensory fibres from the generative organs to the 

 lumbo- sacral cord has not yet been fully made out, but it seems probable 

 that it corresponds to the course taken by the efferent fibres. 



An accessory genital muscle, the retractor penis, which is found in the dog, cat, horse, 

 donkey, hedgehog (not in the rabbit or man), presents considerable physiological 

 interest. It was first described by Eckhard as the Afterruthenband, and consists of a 

 thin band of longitudinally arranged unstriated muscle (15 to 20 cm. long in a spaniel 

 weighing about 15 kilos), which is inserted at the attachment of the prepuce, and is 

 continued backwards in a sheath of connective -tissue to the bulb, when it divides into 

 two slips which pass on either side of the anus. A few striated fibres are found in the 

 back part of this muscle, derived from the external sphincter of the anus and the bulbo- 

 cavernosus muscles. This muscle is extremely sensitive to changes of temperature, 

 and is at the same time very tenacious of life. Thus it may be cut out of the body and 

 kept in serum or blood, in a cool place, for two days. At the end of this time it will, 

 on warming, relax, and enter into spontaneous rhythmic contractions. At about 40 C. 

 the muscle is quite flaccid. On cooling slightly (to 35) it will shorten, and at the same 

 time may enter into slow rhythmic contractions. If cooled to 15 C. the muscle will 

 contract to about a quarter of its previous length. The same shortening may be 

 produced on exciting the muscle with strong interrupted currents. 



The muscle is innervated from two sources, the two nerves having antagonistic 

 actions (cp. p. 247). The motor fibres to the muscle are derived from the lumbar sympa- 

 thetic (i.e. the upper set of nerve-roots), and run to the muscle in the internal pudic 

 nerve. The pelvic nerves, on the other hand, carry inhibitory impulses to the muscle, 

 thus enabling the concomitant vascular dilatation to take effect in producing erection 

 of the penis. 



* Under some circumstances stimulation of the sympathetic nerves may cause 

 relaxation of the uterus. 



