OF DIDELPHYS VIRGINIANA. 109 



pubis, and, there becoming tendinous, joins the tendon of its fellow on the median line. 

 After such unioa of the two muscular parts at nearly right angles with each other, the single 

 delicate terete tendon so formed runs along the whole length of the dorsum of the penis, 

 lying in the median line, to the bifurcation of the glans. Thei'e the tendon also forks or 

 splits in two, and each half runs along the superior margin of the urethral groove of the 

 glans, nearly to the apex of the latter. The important action of this singular muscle, 

 although complicated, is evident. In the first place it has an effect very similar to that of 

 the erector itself, in steadying and straightening, if not actually compressing, the crura. 

 Next, when the penis is protruded backward, and stiff, the muscle causes the organ to 

 point forward, by drawing upon it, until its apex swings around in the arc of a circle whose 

 centre is at the end of the crura. Finally, the terminal splitting of the tendon enables 

 the muscle to draw the forks of the glans apart, so as to insure the entrance of each into 

 its own vagina ; while the attachment of the tendons to the margin of the urethral groove 

 dilates the latter, and facilitates the seminal discharge. The muscle is thus a director as 

 well as a levator of the penis ; and it is certainly very perfectly adapted to the purpose. 



Erector penis. — Each crus is enveloped by a muscular tunic, very similar to those 

 enfolding the capsules of the Cowperian glands. The erectors have no terminal fixed point 

 of origin from the ischiatic ramus. The bony attachment of the muscle is by a fascia from 

 the pubes, near the posterior margin of the symphysis, and distal extremity of the crus ; 

 the muscle is bulbous, or pear-shaped, as it were, being doubled upon itself by returning to 

 near its point of origin after thickening and spreading over the crus, and firmly grasping 

 the latter. It terminates by a stout, laminar tendon, upon the cavernous portion of the 

 penis, close by the bulb. Its action is simple, direct compression of the crus, in much the 

 same way as, e. g., the uterus contracts upon its contents. 



Retractor penis. — There is a pair of muscles for the special purpose of withdrawing the 

 penis into the pelvis upon the subsidence of the priapism. These muscles are remarkably 

 long and slender; being, when extended, some six or eight inches in length, with a width of 

 only about an eighth of an inch, and a thickness of scarcely one-sixteenth. These atten- 

 uated slips arise muscular side by side from the anterior surface of the centrum of the last 

 lumbar, or first sacral, vertebra, and passing along through the pelvis, diverge so as to 

 pass one on each side of the rectum, to which they are imperfectly adherent by condensed 

 cellular tissue. Leaving the rectum, and gaining the root of the penis by direct passage 

 across the slight interval between these two points, they run along the sides of the body of 

 the latter organ, and are finally attached muscular at the outside of the base of the glans, 

 and somewhat upon the under surface, nearly opposite the point of bifurcation. Besides 

 their proper oifice, these muscles have probably some action as reins or stays in guiding or 

 steadying the penis whilst it is erect. 



Accelerator urince. — As the corpus spongiosum, like the corpora cavernosa, has two 

 crura, or begins as lateral halves, giving rise to separate urethral bulbs, this muscle 

 likewise consists of two portions, which, however, meet and coalesce on the median line, 

 beneath the roots of the penis, across which they run in a directly transverse course. The 

 muscle, though small, is distinct ; the two parts, each embracing and compressing a bulb, 

 join across the urethra without a tendinous interval. 



The thick and tumid prostatic part of the urethra, and also the thin anterior membranous 



JIKMOIES BOST. SOC. NAT. HI^T. VOL. II. 23 



