956 



ERECTION. 



i -_ 



The erection -center in the spinal cord is, however, naturally subordi- 

 nate to the dominating vasodilator center in the medulla oblongata, 

 from which connecting fibers pass downward through the cord to the 

 erection-center. Therefore, stimulation of the spinal cord above 

 causes erection, as, for example, by mechanical irritation, asphyxiation, 

 or the use ot muscarin (pathologically also in cases of spinal irritation). 

 Finally, the psychical activity of the brain has a distinct influence upon 

 the genital vasodilators. In the same way as the psychical emotions 

 of anger or shame cause dilatation of the vessels of the head by stimu- 

 lation of the dilators, the direction of the attention to the sexual sphere 

 has an effect upon the erector nerves. This influence of the brain has 



been explicable since the de- 

 pendence of the local lumen of 

 the vessels upon the cerebral 

 cortex has been known. From 

 the cerebral cortex the fibers 

 whose irritation Eckhard ob- 

 served to cause erection prob- 

 ably pass through the cerebral 

 peduncles and the pons. 



If, thus, the impulse to erec- 

 tion is given by the arterial 

 fluxion, the complete develop- 

 ment of the process may take 

 place through the activity of the 

 following transversely striated 

 muscles : 



i . The ischiocavernosus 

 muscle (Fig. 108) arises from 

 the ischium, and surrounds the 

 root of the penis by its tend- 

 inous union like a sling. In 

 its contraction it compresses 

 the root of the penis from 

 above and the sides, so that the 

 escape of the venous blood is 

 prevented. It has no effect upon 

 the dorsal vein of the penis, as 

 this vessel is protected in the 

 dorsal groove of the penis from 

 the pressure of the tendon. 

 2. The deep transverse perineal 

 muscle is penetrated by the deep 



veins of the penis coming from the cavernous bodies and later uniting with 

 the common pudenal vein and the plexus of Santorini in such a manner 

 that its contraction must compress them between the highly contracted 

 horizontal fibers (Fig. 368, 6). 3. Finally the bulbocavernosus muscle 

 also aids in stiffening the corpus spongiosum, by compressing the bulb of 

 the urethra (Fig. 368, 5 and Fig. 108). All of these muscles can in part 

 be moved voluntarily, and as a result the erection becomes more 

 marked. Under ordinary conditions, however, their contraction follows 

 reflex excitation from the sensory nerves of the penis. 



FIG. 368. Anterior Pelvic Wall with the Urogenital 

 Diaphragm, viewed from in front (externally), after 

 Henle. The corpus cavernosum of the urethra, 4, 

 with the urethra, 3, is divided beneath the point of 

 exit from the pelvis, i, pubic symphysis; 2, dorsal 

 vein of the penis; 5, portion of the bulbocavernosus 

 muscle, arising fsom the perineal septum; t, deep 

 transverse perineal muscle, together with its fascia, f ; 

 6, deep vein of the penis; 7, bulbocavernosus artery 

 and vein. 



