101 



this we have two layers of muscular fibres. The interior is lined with 

 a thin membrane of silvery whiteness, which, when examined micro- 

 scopically, is found to be composed of a series of fibres, covered with 

 a basement of membrane provided with scales of epithelium. 



Beneath this membrane we have a layer of vessels, which are very 

 remarkable for the peculiarity of their arrangement. Near the upper 

 part and on the ventral surface of the bladder, is situated the glandu- 

 lar body before spoken of: it is of an oval figure, somewhat resem- 

 bling in shape an exogenous leaf of that kind termed by the botanist 

 peltate or shield-shaped ; and to this so-called gland, anatomists have 

 assigned the function of secreting the air contained in the bladder. 

 It is largely supplied with blood, for in fact it is made up of little else 

 than bundles of parallel vessels, and with it are connected all the 

 large trunks which supply the whole of the interior of the bladder. 

 The gland receives its supply of blood from the aorta high up, and 

 the artery passes into the bladder immediately over the middle of the 

 gland ; it then divides into a great number of branches, each one of 

 which again divides and subdivides, and ultimately terminates in a 

 brush-shaped appendage, about three lines in length, which is entire- 

 ly composed of a bundle of parallel vessels, which are very minute, 

 (PI. xiii. fig. 3) ; and each vessel, when it has arrived at the free ex- 

 tremity of the gland, bends upon itself and forms a loop, and returns 

 again (fig. 3, a). These parallel vessels are the true capillaries of the 

 gland, and the loops are the points at which the arterial system joins 

 the venous. By a little trouble the whole of this body can be sepa- 

 rated into a series of these brush-shaped appendages, each one of 

 which gives one such an appearance as is represented in PI. xiii. fig. 

 4. When the gland is entire, it presents a slightly lobulated charac- 

 ter, the division into lobules being made apparent by the large trunks 

 going to and from the brush-shaped appendages, which are themselves 

 connected together by the same silvery kind of tissue as that which 

 lines the whole of the interior of the bladder. When the vessels have 

 been well filled, the free surface of the gland is made red by the in- 

 jection ; but in those parts where the injected fluid has not reached 

 the extremity of the brush-like appendages, then it is of a light brown 

 colour. It is loosely connected to the thin lining membrane of the 

 bladder, and can readily be removed with that membrane, the only 

 firm point of attachment being that part where the vessels enter the 

 bladder. The distribution in the other part of the bladder is no less 

 remarkable than it is in the gland. The vessels which take their sup- 

 ply from and return their blood to the gland, are, in the specimen 



