The glans penis of the beaver is cylin drical in shape, but flattened at its extremity, which is studded with large papillm, the • orifice of the urethra being situated near its centre.
In the Guinea-pig, the penis is supported by a flat and slightly curved bone imbedded in its upper portion, which reaches as far as the extremity of the glans above the canal of the urethra. Behind and below the termi nation of the urethral canal is a wide pouch, in the bottom of which are lodged two long cartilaginous horns. This pouch, during erection, is everted, so that the horns pro trude externally. Two tendons are connected with the bottom of' this pouch, which run along the penis inferiorly, and are connected with a thin layer of muscular fibres, derived from the bulb of the urethra and the rami of the corpora cavernosa. These tendons, either by their own elasticity, or by the action of the muscular fibres connected with them, serve to invert the pouch and draw it back again within the glans. The whole surface of the glans is covered with corneous scales, which, with the two horns above mentioned, give it a formidable appearance.
wise in the beaver, only they are of much smaller proportionate size.
In the squirrel, Cowper's glands are repre sented by two large conical bladders twisted upon themselves, the summits of which are evidently of a glandular nature, and are divided internally into numerous small cells. Each of these organs opens by a large orifice into a cul-de-sac, which occupies the interior of the bulb of the urethra, and which is pro longed into a canal, that, becoming gra dually narrower, opens into the urethra near the angle formed by the bend of the penis. The walls of the conical bladders, which con stitute the substance of these glands, contain muscular fibres, which serve to constrict their cavities. In the Alpine marmot and in the boback, these glands present a similar structure.
In the rats they are of very large size and of a pyriform shape, their substance being en veloped in an aponeurotic sheath.
Penis. — The penis in the Rodentia is dif ferently arranged in different genera. In the Guinea-pig and the agouti, this organ, after running forwards in the ordinary manner as far as the anterior margin of the symphysis pubis, bends back again upon itself' beneath the skin of that region towards the anus, so that the opening of the prepuce is situated very little in front of the anal orifice. Mus
cular fibres, derived from the crenlaster mus cles, are inserted into the penis near its curva ture ; and others, derived from the external oblique muscle of the abdomen, are connected with the same point. The former probably contribute to effect the protrusion of the penis from its sheath, whilst the latter draw it back again into its concealment.
In the marmot, the penis, when it arrives in the sub-pubie region, does not bend back again to approximate the anus, but curves directly downwards ; in which position it is retained by ligamentous attachments.
In many genera of Rodents, as,for example, in the rats, the voles, the dormice, the jerboa, the hares, and the lagomys, the penis, after issuing from the pelvis, does not run forwards beneath the symphysis of the pubis, but passes directly backwards towards the anus, imme diately in front of which the orifice of the prepuce is situated ( fig. 281. a).
In most of the Rodentia the penis contains a bone, imbedded in the substance of the corpus cavernosum. But the most remark able part of the penis in the order before us, is the glans, which in many species is armed with such a formidable apparatus of spines, saws, and horny spikes, that it rnust indeed be a rather stimulating instrument of excitement.
In the Alpine marmot it is conical, and terminated by a sharp point, formed entirely by the extremity of the os penis. On the right of this point is situated the opening of the urethra, and on the left there is a small but deep cul-de-sac.
In the comrnon rat, the extremity of the penis, in its relaxed state, resembles a second prepuce, there being here a wide cavity exca Yet even this is an innocent weapon when compared with the penis of the agouti and other allied genera, which, besides containing a pouch inclosing strong horny spikes like that of the Guinea-pig, has the whole surface of the glans covered with sharp recurved spines, and is, moreover, provided on each side with a broad plate of horn, adherent to the glans by its inner border, while all its outer ftee edge. is armed with strong sharp teeth resembling those of a saw (fig. 285.) ; a structure which is additionally remarkable from the circumstance, that in the females of the species thus barbarously armed, the vagina offers no peculiarity in its appearance.