142 



PHYSIOLOGY 



CHAP. 



more or less completely, the interior of the vessel, aiid limits the 

 alllux of blood to the corpora cavernosa whenever the strong 

 muscular coat assumes the tonus which exists when the penis 

 is flaccid. The muscular fibres also of the trabeculae of the 

 cavernous tissue which bounds the spaces must contribute to 

 restrict the capacity of these, during the state of tonicity which 

 exists during the flaccid state of the penis. When, therefore, all 

 the muscular elements, whether of arteries or of trabeculae, con- 

 tract actively, as happens for instance during a cold bath, there is 

 observed a diminution in the size of the penis to about one-sixth or 

 one-fifth its volume in its general state of flaccidity ; this fact demon- 

 strates that in these circumstances the penis empties itself almost 

 completely of the blood contained in the vessels or in the cavernous 



spaces. When, however, sexual 

 excitement begins, all the muscu- 

 lar fibres with which the penis 

 is provided expand actively, the 

 helicine arteries lengthen and 

 become distended, the little val- 

 vular cushions with which they 

 are provided are drawn back ex- 

 centrically, the cavernous spaces 

 dilate, and the blood impelled by 

 the rhythmic action of the heart 



penetrate freely from the 

 .* . , ,, 



fibres and membranes were coloured in the arteries into the Corpora CaVCmOSa 

 preparation. (Eberth.) Magnified 132 11Tlf l PT . af rnno . r>rpsnrp nnrl ViriTirr 

 diameters, a, tunica adventitia ; m, tunica Under Strong prefi T6, and t ring 

 * muscularis ; ei, internal elastic membrane ; abnnt, hhnf, OTPflt", inprpfl^p in tVip 

 c, little valvular cushions of the intima, auoul ' T 



projecting into cavity and traversed by Volume and rigidity 01 the peniS 

 elastic lamellae; e, elastic lamella at -i r -u j j * 



periphery of cushion. which is observed during erection. 



Numerous experiments were 



carried out to illustrate the changes which the circulation of 

 the blood in the penis undergoes during erection. This im- 

 portant phenomenon which renders sexual intercourse possible, 

 needs a short historical account. Regner de Graaf was the 

 first in 1668 to produce erection of the penis in the dead body 

 by injection of the vessels ; he saw that it increased by four 

 or five times its volume, became hard, and curved on the dorsal 

 surface, erecting itself and adapting itself to the curve of the vagina 

 into which it must be introduced during coitus. The increase in 

 size and rigidity of the penis depends essentially, therefore, on 

 the forcible filling and tension of all its blood-vessels and cavernous 

 spaces, and its erection does not depend on the contraction of any 

 muscle, but is a passive mechanical effect, due to the fact that 

 the dorsal fascia of the penis is more tense, being shorter, than 

 the ventral, on account of which the penis must necessarily be 

 curved dorsally and erected when it increases in size and length. 



FIG. 35. Transverse section of an artery of can 

 the bulb of urethra of man ; the elastic 



