ERECTION OF THE PENIS. 



857 



652). The capsule becomes more and more fused with the ovarian stroma. If pregnancy does 

 not take place after the menstruation, then the fatty matter is rapidly absorbed, and the effused 

 blood is changed into harmatoidin ( 20) and other derivatives of haemoglobin, while there is a 

 gradual shrivelling of the whole mass, which is complete in about four weeks, only a very 

 small remainder being left. Such a corpus luteum, i.e., one not accompanied by pregnancy, is 

 called a false corpus luteum. If, however, pregnancy occurs, then the corpus luteum, instead 

 of shrivelling, grows and becomes a large body, especially at the third and fourth month, the 

 walls are thicker, the colour deeper, so that the corpus luteum at the period of delivery may be 

 6 to 10 mm. in diameter, and its remains may be found in the ovary for a very long time thereafter 

 (fig. 651). This form is sometimes spoken of as a true corpus luteum. [We cannot draw a sharp 

 distinction between these two forms.] Only a very small number of the ova in the ovary 

 undergo development and are discharged ; by far the greater number degenerate (Slavjansky). 



436. PENIS EBECTION. Penis. [The penis is composed of the two long cylindrical 

 corpora cavernosa, the corpus spongiosum, which lies between and below them, and sur- 

 rounds the urethra ; these are held together by fibrous and muscular sheaths, and are 

 composed of erectile tissue.] Our knowledge of the distribution of the blood within the 

 penis is chiefly due to C. Langer's researches. The albuginea of the corpus spongiosum con- 

 sists of tendinous connective-tissue, containing thickly- woven elastic tissue and smooth 

 muscular fibres, which together form a solid fibrous envelope, from which numerous interlacing 

 trabecular pass into the interior, so that the corpus spongiosum comes to resemble a sponge. 

 The anastomosing spaces bounded by these trabecular form a series of inter-communicating 

 venous spaces or sinuses filled 

 with blood and lined by a layer . \\ 



of endothelium constituting erec- /'/ iVvIl 



tile tissue (fig. 653). The largest <\l m 



sinuses lie in the lower and 

 external part of the corpus caver- 

 nosum, while they are less nume- 

 rous and smaller in the upper 

 part. The small arteries arise 

 from the A. profunda penis, which 

 runs along the septum, and pass 

 to the trabecular after following a 3 

 very sinuous course. At the outer 

 part of the corpus spongiosum, 

 some of the small arteries become 

 directly continuous with the larger 

 venous sinuses ; some of them, 

 however, terminate in capillaries 

 both in the outer part and within 

 the corpus spongiosum, the capil- 

 laries ultimately terminating in 

 the venous sinuses. The helicine 

 arteries of the penis described 

 by Joh. Muller are merely much 

 twisted arteries. The deep veins Y\v. 653. 



of the penis arise by fine veinlets , .. , . t __, . - , . , . .,, , , . 



within the body of the organ, Erectile tissue a, trabecular of connective-tissue with elastic 



while the veins proceeding from fibres and smooth muscle ( c ) 5 b > venous 8 P aces ' 



the cavernous spaces pass to the dorsum of the penis to form the vena dorsalis penis. As these 

 vessels have to traverse the meshes of the vascular network in the cortex of the corpora 

 cavernosa penis, it is evident that, when the network is congested by being filled with blood, 

 it must compress the outgoing venous trunks. The corpus cavernosum urethrar consists for 

 the most part of an external layer of closely packed anastomosing veins, which surround the 

 longitudinally directed blood-vessels of the urethra. 



In the dog, all the arteries of the penis run at first towards the surface, where they divide 

 into penicilli. The veins arise from the capillary loops in the papillae, and they empty their 

 blood into the cavernous spaces. Only a small part of the blood passes to the cavernous spaces 

 through the internal capillaries and veins, but arterial blood never flows directly into these 

 spaces (M. v. Frey). 



Mechanism of Erection. Erection is due to the overfilling of the blood- 

 vessels of the penis with blood, whereby the volume of the organ is increased 

 four or five times, while, at the same time, there are also a higher temperature, 

 increased blood-pressure (to \ of that in the carotid Eckkard), with at first a 

 pulsatile movement, increased consistence, and erection of the organ. 



