=M. bulbocavernosus= (=accelerator urinæ=) (_l_).--The two muscles cover the ventral surface of the penis. _Origin_ of each from a median raphe, which passes from the bulbous portion of the urethra toward the anus. The fibres pass toward the distal end of the penis and have their _Insertion_ into the distal half of the lateral surface of the corpus cavernosum penis. =M. compressor urethræ membranaceæ= (_n_).--A thick layer of striated muscle-fibres which surrounds the urethra between Cowper’s gland (3) and the prostate (4). The fibres have a circular course, and the cranial ones are attached to the crura of the penis. The other fibres have no fixed attachment. _c. Muscles Peculiar to the Female_ (Fig. 114).--=M. levator vulvæ= (Strauss-Durckheim), or =constrictor cunni= (_b_).--This is homologous with the levator scroti of the male. It consists of a band of fibres which pass ventrad from the external sphincter ani (_a_) and surround the vulva (3), lying immediately beneath the integument. =M. constrictor vestibuli=, or =rectovaginalis= (Strauss-Durckheim) (_d_). [Illustration: FIG. 114.--MUSCLES OF THE ANUS AND UROGENITAL ORGANS IN THE FEMALE. _a_, M. sphincter ani externus; _b_, M. levator vulvæ; _c_, M. sphincter ani internus; _d_, M. constrictor vestibuli; _e_, M. ischiocavernosus (cut); _f_, M. urethralis; _g_, M. caudoanalis; _h_, M. caudovaginalis; _i_, M. transversus perinei; _j_, M. caudorectalis. 1, the tail; 2, anus; 3, vulva; 4, rectum; 5, vagina; 6, neck of the bladder.] _Origin_ from the sides of the sphincter ani internus (_c_). The muscle forms a distinct bundle two or three millimeters wide, which passes ventrocaudad and is _inserted_ into the ventral surface of the urogenital sinus, caudad of the insertion of the ischiocavernosus (_e_). =M. caudovaginalis= (Strauss-Durckheim) (_h_).--A slender band just craniad of the caudoanalis (_g_), and corresponding to the caudocavernosus of the male. _Origin_ from the median line of the ventral surface of the first two caudal vertebræ. The muscle passes caudoventrad, lying between the levator ani and the caudorectal (_j_), and is _inserted_ into the ventral side of the urogenital sinus, at the base of the clitoris. =M. urethralis= (_f_).--This consists of fibres surrounding the cranial part of the urogenital sinus and the caudal parts of the vagina and neck of the bladder. _Origin_ partly on the caudal part of the symphysis of the ischium, partly from the ventral surface of the urogenital sinus, where the fibres are attached to the corpora cavernosa clitoridis. The fibres pass dorsad over the surface of the sinus, and over the surface of the union of the vagina and neck of the bladder, to be inserted into the sides of the vagina and the dorsal surface of the urogenital sinus. THE CIRCULATORY SYSTEM. I. THE HEART. COR.