or circumference of the sheath 40 additionally more than one band 44 interspaced by predetermined distances along the sheath can be used the sheath shown in fig6 also incorporates another variation which is applicable to all forms of sheath shown by the drawing specifically this sheath 40 is open at both ends with respective elastic end rings 46 48 referring now to fig7 13 a fourth embodiment of the invention for assisting erectile function is shown in which the facilitator comprises a sheath which also preferably functions as a prosthetic device for individuals who can only maintain a partial erection referring specifically to the form shown in fig7 sheath 50 includes central and proximal thickened portions 52 54 concentric about longitudinal axis a and having a thickness greater than that of the remainder of the sheath 50 preferably between about 2 and 15 mm for example in fig7 thicker portions 52 54 are solid and is preferably comprised of a synthetic polymer such as latex or silicone the relatively greater depth of the thickened portions 52 54 results in a degree of elasticity less than that of the remainder of the sheath 50 such that an erection is maintained by imparting an external pressure onto the central and rear portions of the penis to impede venous blood outflow additionally the greater depth of thickened portions 52 54 provides structural support of the penis for individuals who can only obtain partial erections thus sheath 50 also functions as a prosthesis the relative depth of thickened portions 52 54 as well as the relative elasticity of thickened portions 52 54 is determined by the relative diameter of the user 39 s penis the degree of external pressure desired to be imparted as well as the.