230 ANATOMY OF VERTEBRATES. 



§ 162. Spleen of Birds. — The spleen, figs. 85, 87, s, s, is com- 

 paratively of small size in Birds ; it is generally of a round or 

 oval figure, but sometimes presents an elongated and vermiform 

 shape, as in the Sea-GuU, or is broad and flat as in the Cormo- 

 rant. It is situated beneath the liver, on the right side of the 

 proventriculus. It is, however, somewhat loosely connected to 

 the surrounding parts, so that its position has been differently 

 described by different authors. A process of the pancreas com- 

 monly passes into close contact, and is connected with the spleen 

 by a continuation of vessels, as in the Hornbill, fig. S7, q, s. The 

 texture of the spleen is closer in Birds than in Mammals ; but a 

 minute examination proves that the blood of the splenic artery is 

 ultimately deposited in cells, from which the splenic veins arise. 

 These veins in the Swan and some other Lamellirostres form a 

 network on the exterior surface of the spleen, as in the Chelonian 

 Reptiles. 



In many Birds, as e.g. Vultures, Falcons, the Starling, Magpie, 

 Heron, Bustard, and in most Aquatic Birds, two small bodies are 

 found, one on each side of the trachea, very near the lower larynx 

 and frequently attached to the jugular veins. They may be homo- 

 logues of the ' thyroid gland.' In addition to these there are two 

 similar bodies, in the Gannet, attached to the upper part of the 

 commencement of each bronchus. 



§ 163. Peculiar Secretions. — The unctuous fluid mth which Birds 

 lubricate their feathers is secreted by a gland situated above the 

 coccyx or uropygium. This gland consists of two lateral moieties 

 conjoined. As might be expected, it is largest in the birds which 

 frequent the water. In the Swan it is an inch and a half in length, 

 and has a central cavity, which serves as a receptacle for the accu- 

 mulated secretion. Each lateral portion is of a pyriform shape, 

 and they are conjoined at the apices, which are directed backward, 

 and are perforated by numerous orifices, encircled in some birds 

 by a crown of feathers. The longitudinal central cavities present 

 numerous angular openings, in which there are still smaller ori- 

 fices of the secerning follicles. These consist of close-set almost 

 parallel straight tubules, extending to the superficies of the gland, 

 mthout ramifying or intercommunicating, and preserving an 

 equable diameter to their blind extremities. The tubules are 

 longest at the thickest part of the gland, and become shorter and 

 shorter towards the apex. 



The follicles to which is due the peculiar odour of certain birds, 

 as e. g. the Hoopoe, Muscovy Duck, Black Vulture, &c., are pro- 

 bably somewhat diffused on parts of the integument. 



