MUSCLES OF MALE GENITALIA
1. Note the functions for the cremaster muscle, the urethralis and bulbospongiosus muscles, the ischiocavernosus muscles, and the retractor penis muscles.
The cremaster muscle is formed from the caudal fibers of the internal abdominal oblique muscle.
It passes through the inguinal canal and attaches to the outer aspect of the parietal vaginal tunic (see Figures 14-6 and 14-7). This muscle pulls the testis up against the superficial vaginal ring, particularly in cold weather. The cremaster muscles are responsible for the testes being drawn into the abdominal cavity of the elephant, deer, and rabbit during times other than the breeding season.A skeletal muscle, the urethralis (see Figure 14-1), is the pelvic continuation from the smooth muscle wall of the urinary bladder. Peristaltic action of this muscle assists in the transport of urine or semen through the pelvic urethra.
The bulbospongiosus muscle (Figures 14-1 and 14-13) is a striated muscle continuation of the urethralis. It continues throughout the length of the penis in the horse, but only proceeds for a short distance along the penile urethra in other animals. The bulbospongiosus muscle continues the action of the urethralis in emptying the urethra.
■ FIGURE 14-13 Penis of the bull and some of its associated muscles. The bulbospongiosus muscle assists in emptying the urethra. The ischiocavernosus muscle assists in the erection process and the retractor penis muscle assists in the return of the penis to the prepuce after intromission.
The ischiocavernosus muscles are paired, striated muscles that converge on the body of the penis from their origins on the lateral sides of the ischial arch (see Figures 14-1 and 14-13). When these muscles contract, they pull the penis upward against the floor of the pelvis. Much of the venous drainage from the penis is obstructed because of the location of the veins on the dorsal surface of the penis and erection is thereby assisted.
The retractor penis muscles are paired striated muscles that originate from the suspensory ligaments of the anus. They continue forward and converge caudal to the body of the penis (see Figures 14-12 and 14-13). After they join on the underside of the penis, they continue forward to the glans penis or sigmoid flexure. The retractor penis muscles pull the flaccid penis back into the prepuce.
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