OCR Text |
Show 1877.] BURSA FABRICII IN BIRDS. 311 had lived in the Society's Gardens for eleven years. As a rule, the central cavity of the bursa becomes diminished and the communication with the cloaca obliterated in the process of atrophy ; and finally, in some cases at least, the whole organ completely disappears, losing its characteristic form and structure, and becoming fused with the tract of abdominal aponeurosis that covers the back wall of the alimentary canal, ultimately forming a flat riband-like, or round cordlike, ligamentous structure. Spangenberg observed the conversion of the bursa Fabricii into a round cord-like ligament in the Duck ; and Alesi hasobserved it (and described it minutely,with figures showing the histological changes that go on) in the Fowl. He sums up the process of atrophy in the last-named bird as follows :-The epithelium which covers tbe internal surface of the bursa becomes, as it were, invaginated into the thickness of the mucous layer, becoming pressed in between the lymphatic follicles. The connective tissue between the latter increases rapidly in bulk, and becomes full of numerous small oval corpuscles ; at the same time the follicles become absorbed, and the whole of the bursa becomes obliterated and fused with part of the abdominal aponeurosis. The epithelium gradually becomes confined to certain irregular tracts in the thickness of the mass of connective tissue ; but even these disappear finally. The process of atrophy in the other species which he observed is essentially the same as that in the Fowl. I now proceed to describe the general characters of the bursa Fabricii in the groups of birds I have examined. In the Passeres it is usually small, pyriform, with a small opening and glandular walls without ridge-like elevations on the interior. It seems to disappear completely in adult birds. In the Rhamphastidee : dis- Fig. 3. - CO Cloaca and Bursa of Geococcyx affinis. The cloaca is cut short and laid open from before. The narrow peduncle of the bursa is supposed to be seen through the cloaca, a. " Vesical sphincter. b. Bursa, c. Opening of same, d, d'. Ureter and opening, e, e. Vas deferens and opening. appears in the adult, only leaving a small pore to mark its place of opening. In the Cuculidce it presents a very characteristic shape, the peduncle being long and thin, and the extremity club-shaped, |