122 AVES. 



found, situated on the mesial line of the anterior extremity of the 

 kidneys, are in contact externally with the large vascular trunks, and 

 are partly covered by the testes and ovaria. 



PARTICULAR ORGANS OF SECRETION. 



PARTICULAR glandular organs are found very generally distributed 

 in the region of the tail and cloaca ; but really specific secretions, 

 such as occur so frequently in several of the orders and genera of 

 Mammalia, do not appear to occur in Birds. 



A peculiar gland, which is called the Glandula Uropygii, exists 

 very commonly throughout the class, and secretes an oily fluid of a 

 whitish or yellowish color, having occasionally a musky odor, 

 and which is applied by the bill to anoint the feathers, so as to 

 prevent their getting wet. It is situated above the last caudal 

 vertebrae upon the quills of the remigial feathers of the tail, and 

 consists properly of two distinct glands, which are either united in 

 the median line, or frequently only by their posterior extremities. 

 They consist internally of close-set elongated coecal tubules, not in- 

 tercommunicating and opening into a mostly linear cavity of greater 

 or less size situated in the centre of the gland. A double orifice, 

 rarely one (or many, as in the Pelican, where twelve apertures are 

 found arranged in two rows), which opens upon a papilla, and, as 

 in the Diurnal birds of Prey, the Parrots, Gallinse, and Natatores, is 

 surrounded by a tuft of small feathers, indicates the outlet of the 

 excretory duct. The gland itself is usually triangular or cordiform in 

 the Natatores, as the Ducks, where it is of the largest size, and divi- 

 ded by a fissure into two clavate lobes. It is very rarely absent, as 

 in the Brevipennes, e. g. the Bustard, in the Penguin, and some only 

 of the American Parrots, for others possess it. 



Another organ that may be conjectured to be one of secretion 

 also, is called the Bursa Fabricii. It occurs in nearly all Birds, 

 being wanting in the Ostrich, probably alone among the Brevipen- 

 nes, and is situated deep within the pelvis between the ureters and 

 behind or above the cloaca, in front of the extremity of the sacrum, 

 and is usually covered by cellular and adipose tissue. It opens 

 below the two ureters into the cloaca by a considerable orifice, which 

 is separated by a fold from the urinary compartment of that cavity. 

 Covered externally by a layer of muscular fibres, it is in some cases 

 of a thin membranous texture, but in others frequently provided with 

 a thick layer of small follicles, as is especially the case in the Grallae 



