ON THE BURSA FABRICII IN BIRDS. 9 



opens by a simple rounded orifice without any valve* into the cloaca at P ' Z '|^g 877 ' 

 the point already indicated. The bursa lies on the posterior wall of the 

 cloaca (to which it is usually attached by a kind of aponeurosis) in the 

 space between the cloaca and the pelvis. This disposition of parts, as 

 seen from behind, is shown in fig. 2, in the common Guillemot. The 



Fig. 2. 



~d 



Back view of Cloaca of Uria troile. 

 a. Bursa Fabricii. b. Oviduct. c, c. Ureters. d. Sphincter muscles. e. Caeca. 



bursa when laid open frequently contains faecal matter, more or less 

 hard, or may be empty. The walls may be thin, as in the Passeres, 

 Parrots, &c., or thick and markedly glandular, as in the Gallinae, 

 Herodiones, &c. The bursa is usually constricted below into a narrow 

 peduncle, with a narrow central channel ; above, the contained cavity is 

 more considerable but of varying dimensions. 



Signor Alesi, in the paper already referred to, has described at great 

 length the minute structure of the bursa Fabricii in the common Fowl 

 and some other birds. I must here content myself with giving a brief 

 resume of his conclusions as regards the histological structure of the 

 organ in question. A transverse section of the wall in the neighbour- 

 hood of one of the ridges into which, in the Fowl and allied forms, the 



* Barkow, I. s. c., describes the lower part of the peduncle of the bursa as projecting 

 into the cloaca in the common Fowl, and there forming a conical sort of flap (Zipfel) 

 over the opening. I have never myself seen any thing like this " Zipfel " in any bird 

 I have examined ; and all other writers are equally silent on the point. Most, indeed, 

 say expressly that there is no valve or flap of any kind. 



