20 
DR. H. GADOW ON THE CLOACA AND ON THE 
structure as the previous one, but with softer walls. Into it opens in the medio 
ventral line the Jong-necked bladder, and near the dorso-median line open on each 
side, near the base of a papilla, the ureters and the genital ducts. In the female 
there is one opening only for the oviduct and for the ureter of each side. This 
urodseum, or urino-genital chamber, is as usual shut off from the rectum by a high 
circular fold. Peritoneal canals are indicated by two recessus of the body cavity, 
which laterally, from the urino-genital orifices, extend into the cloacal wall, and below 
the fold F end each in a small non-perforated papilla. The latter were best developed 
in the male, and are represented in fig. 12. 
The Avian type (figs. 14, 15, 16, 20, 21) is an interesting modification of both the 
crocodilian and the saurian arrangement. The determination of the various chambers 
is beset with difficulties because of the extreme variability of the separating folds. 
The whole cloaca of most birds is divisible into a vestibulum, a urino-genital or 
middle chamber, and a rectal or innermost chamber. 
The middle or urino-genital chamber is small ; it receives in its dorso-lateral walls 
the ureters and the genital ducts, which are frequently protected by papillae. Imme¬ 
diately above (headwards from) the uretro-genital orifices is a circular fold rc, most 
prominent on the ventral side ; below the orifices, i.e., towai’ds the tail, is always 
present a well-marked fold F (sphincter vesical of Martin-St.-Ange), best developed 
on the dorsal and lateral sides, whilst towards the ventral aspect it goes over into the 
coating of the copulatory organ, when such is present; sometimes, however, the fold 
is nearly circular, and very distinct. The room between this fold and the outer anal 
opening is homologous with the vestibulum of other Amniota; it lodges the copula¬ 
tory organ ; a wide opening in its dorsal wall leads into the bursa Fabricii. The 
entrance to this pouch is sometimes, e.g., Struthio and Leptoptilus, guarded by a 
valvular fold, and divides the whole of the vestibulum, according to Geoffroy, into a 
bourse da 'prepuce and a bourse accessoire (bursa Fabricii) ; this fold is, however, 
unimportant, and absent in many birds. That the bursa often forms a mere dorsal 
dilatation of the vestibulum has been shown and explained by Forbes. .Near the 
sides of the penis, in various positions, are often found in both sexes glandular pores 
(Cowfer’s glands, Geoffroy), reminding us of similar pits in the Crocodile. They 
occur, however, also in birds which possess no copulatory organ, and seem, therefore, 
to belong to the vestibulum itself; their analogy with anal glands of other vertebrata 
seems remote. The third chamber is situated above the urino-genital one, and this 
presents some difficulties. In most birds it forms an oval dilatation of the rectum, 
and is of considerable size. In Casuarius and Rhea it goes gradually over into the 
rest of the rectum, and its inner walls agree in structure with the latter, but in many 
Carinatse, and in Struthio, the cephalic end of this chamber is marked by a very well 
developed circular fold and sphincter-like constriction, and, in connexion with this, the 
inner structure of the walls is smooth and very different from that of the rectum. 
Transitional stages are, however, numerous. Moreover, in Struthio this chamber is 
