REPRODUCTION IN MAN 1375 



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-caver- 

 nosus 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. 276). The motor fibres to the muscle are derived 

 from the lumbar sympathetic (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. 



