The vesiculce sendnales, or their analogues, exist in all the Rodentia. In the hares they are simple bags (fig. 281. d); but, generally speaking, their cavity is more or less convo luted, or branched out into catca, as, for ex ample, in the agouti (fig. 282. i, i), and in the beaver (fig. 284. o, p). In most of the genera of this order of quadrupeds the vesiculm seminales are remarkable for their great de velopment ; in the Guinea-pig they form two long conical tubes, which taper much towards their extremities, but are slightly sacculated for a portion of their length ; the excretory ducts in this animal open into the urethra by an orifice common to them, and to the vasa deferentia.
In the agouti each opens separately into the common cavity of the verumontanum, in which are also situated the separate orifices of the vasa deferentia, and of the excretory' canals of the accessory vesicles ; so that all In the hare and in the rabbit these organs are represented by the single sac already alluded to (fig. 281. d), the size of which is considerable ; this sac is of a triangular shape, two of its three corners being sometimes con siderably elongated ; its walls are membranous, except for about two thirds of its upper side, where they are formed by a thick glandular substance something resembling in texture the prostate gland. This sac opens into the urethra by a single orifice excavated in the centre of the yerumontanum, which receives likewise the terminations of the two vasa dere rentia.
In the lagomys (Lepus pusillus, ogotonus, and alpinus, Pall.) the vesiculm seminales are double and separate.
In the common squirrel each seminal vesicle consists of a short canal folded upon itself. This approximates its fellow on the opposite side between the prostate and the canal of the urethra ; and, contrary to what is usual in this order, internal to the vasa deferentia.
The prostate glands.— The name of pro state gland is restricted by Cuvier to those glandular masses of analogous structure to the human prostate, the excretory canals of which open by one or several orifices into the com mencement of the muscular portion of the urethra, or into the first portion of that canal. In some cases, however, the representatives of the prostate are made up of numerous rami fied and complicated tubes, in which case they are called tubular prostates. In the hare and
the rabbit, this gland is represented by the glandular mass, which, as above described, forms a portion of the walls of the vesiculae semi nales, and which extends for some distance upon the muscular portion of the urethra (fig. 281. c).
which, however, it is only adherent at the two points where its excretory ducts penetrate that canal ; in this animal its shape is oval, flattened above, and bilobed posteriorly.
In the agouti the prostates (fig. 282. e,e) assume the tubular form, each gland being composed of a common trunk, divided into branches and ramusculi, ending in vascular enlargements.
In the numerous family of rats, the pro states are represented by several packets of ramified tubes, situated around the com mencement of the canal of the urethra. Two others are connected with the inferior surface of the vesicul seminales : these consist of a principal trunk, which has but few ramifica tions. These latter organs exist likewise in the lagomys, and may perhaps be considered accessory seminal vesicles.
The Guinea-pig is furnished with numerous ramified and convoluted tubes, connected to gether by a loose cellular tissue,which occupy the situation of the prostate gland ofother quadrupeds.
In the Alpine marmot it forms a consider able mass situated above the commencement of the urethra, divided posteriorly into two roundish lobes.
In the squirrel the prostate gland is as long as the muscular portion of the urethra, to Cowper's glands. Most of the Rodentia are provided with accessory glands, which, in situation at least, correspond with those called the glands of Cowper in the human subject.
In the male Agouti, these glands are two round, flattened, and very vascular bodies (fig. 282. o), which open into the bulb of the urethra by separate ducts (p). In the Guinea-pig their structure is similar, as like vated in the centre of the glands, enclosing a bone, the extremity of which projects beyond it, and is furnished with two small, cartila ginous, lateral appendages. Beneath this is situated the cavity of the urethra. Most of the genera allied to the rats, such as the hamsters, the voles, the dormice, &e., have their penis constructed upon the same plan ; but in some the surface of the glans is smooth, whilst in others it is covered with or studded with fine hairs.