602 



AVES BIRDS. 



notice. Two sets of ducts are provided for this purpose : the 

 first (Jig. 73, i) carries the bile directly from the liver into the 

 gall-bladder (g), from which another duct conveys the bilious fluid 

 into the duodenum ; but the second set of bile-vessels conducts 

 the secretion of the liver at once into the intestine by a wide 

 canal (o), that has no communication whatever with the gall- 

 bladder, there is, therefore, no arrangement like that of the 

 " ductus communis choledochus" of Mammals : if the bile is want- 

 ed immediately, it passes at once into the intestine through the 

 duct o ; but, if digestion is not going on, it is conveyed into the 

 gall-bladder through the duct i, to be there retained until needed. 

 The pancreas (Jig. 218, e, e) is a conglomerate gland of con- 

 siderable size, situated in the elongated loop formed by the duo- 

 denum : it generally consists of two portions more or less inti- 

 mately connected, and from each portion an excretory duct (n) is 

 given off; these two ducts terminate separately in the intestine, in 

 the immediate vicinity of the openings of the biliary canals. In 

 some birds even three pancreatic ducts are met with, as is the case 

 in the common fowl ; but under such circumstances the third duct, 

 instead of opening into the intestine at the same point as the 

 other two, issues from the opposite extremity of the pancreas, and 

 enters the middle of the duodenum at the place where the gut 

 turns upon itself. 



The spleen (Jig. 273, f) is of very small size in all birds ; it is 

 situated near the anterior extremity of the pancreas, and is loosely 

 connected to the side of the proventriculus (b). The distribu- 

 tion of its vessels, and its general structure, is the same as in 

 Mammalia. 



The lymphatic system is well developed, and the course of 

 the lymphatic vessels has been investigated with great care by 

 various anatomists. The vessels themselves are thin, and have but 

 few valves ; they principally accompany the larger blood-vessels 

 from all parts of the body to the aorta, around which they form a 

 plexus, and ultimately join to give rise to two principal trunks or 

 thoracic ducts: these terminate severally in the right and left 

 jugular veins, and into these vessels the greater proportion of the 

 lymph and chyle absorbed is of course poured, to be mixed with 

 the circulating blood. 



(671.) Before describing the circulatory apparatus of birds, it will 

 be advisable in the next place to consider the nature and disposition 

 of their organs of respiration ; which, from what has been already 



