AVES. 



327 



(see fig. 165, where x represents the orifice by 

 which the bile pusses both in and out of the 

 gall-bladder.) 



In the Goose the cyst-hepatic duct termi- 

 nates by a very small orifice, surrounded 

 by a smooth projection of the inner mem- 

 brane, which, aided by the obliquity of the 

 duct, acts as a valve and prevents any re- 

 gurgitation towards the liver. The cystic duct 

 here passes abruptly from the posterior ex- 

 tremity of the gall-bladder, which is not pro- 

 longed into a neck. The duct makes a turn 

 round the end of the bag, and is so closely ap- 

 plied to it, as to require a careful examination to 

 determine the true place of its commencement. 



The hepatic duct fn, fig. 165) arises by two 

 branches from the large lateral lobes of the 

 liver, which unite in the fissure or ' gates' of 

 the gland. Two hepatic ducts have been found 

 in the Curassow; but these and the cystic 

 duct terminate separately in the duodenum. 



The place of termination of the cystic and 

 hepatic duct is generally, as shown in Jig. 163 

 and 165, pretty close together at the end of 

 the fold of the duodenum ; but in the Ostrich 

 one of the hepatic ducts, which is very large 

 and short, terminates in the commencement of 

 the duodenum about an inch from the pylorus; 

 while the other enters with the pancreatic duct 

 at the termination of the duodenum. 



Both the cystic and hepatic ducts undergo 

 a slight thickening in their coats just before 

 their termination; and it is remarkable that, 

 in some of the Marsupiata, as the Kangaroo, 

 the termination of the ductus choledochus is si- 

 milarly thickened and glandular. The passage 

 of the bile-ducts in birds through the coats 

 of the intestine is oblique, as in the Mam- 

 malia, and they terminate upon a valvular 

 prominence of the lining membrane of the gut. 



The Pancreas (q, q, Jig. 163, 165) consists 

 of two and sometimes of three distinct por- 

 tions in Birds; but these are so closely ap- 

 plied together at some point of their surface 

 as to appear like one continuous gland. It 

 is of a narrow, elongated, trihedral form, lodged 

 in the interspace of the duodenal fold, and 

 generally folded upon itself like the duodenum, 

 as in the Hornbill (fig. 165). 



The structure of the pancreas is conglome- 

 rate, like that of the salivary glands, but the 

 ultimate follicles are differently disposed. In 

 the salivary glands these are irregularly 

 branched, while those of the pancreas in Birds 

 diverge in the same plane from digitated and 

 pinnatifid groups.* 



The ducts (r r, Jig. 163, 165) formed by 

 the reiterated union of the efferent branches 

 from the component follicles of the pancreas 

 are in general two in number, which terminate 

 separately in close proximity to the hepatic 

 and cystic ducts ; but occasionally there are 

 three pancreatic ducts, as in the common Fowl, 

 Pigeon, Raven, and Horn-bill ; in which case 

 the third duct commonly terminates at a dis- 

 tance from the other two: in the Horn-bill 

 it proceeds from an enlarged lobe of the pan- 



* Mullcr dc Gland. Struct. Pen. fol. p. 66. 



creas at the end of the duodenal fold, and 

 entering that part, as ut ?', Jig. 165. 



The Spleen (s, s, Jig. 163, 165) is compara- 

 tively 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-Gull, or is broad and flat as in the Cor- 

 morant. 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. 

 We have generally been able to trace a pro- 

 cess of the pancreas passing into close contact 

 with it, and connected to it by a continuation 

 of vessels, as in the Horn-bill (fig. 165, <?, s), 

 where it has been turned aside to show the 

 hepatic and pancreatic ducts. The texture of 

 the spleen is much closer in Birds than in 

 Mammalia; but a minute examination proves 

 that the blood of the splenic artery is ulti- 

 mately 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. 



Absorbents. The presumed absence of ab- 

 sorbent vessels in the Oviparous Vertebrata was 

 cited by the supporters of the theory of venous 

 absorption in the time of William Hunter as 

 strong evidence in favour of their views ; and 

 the same assertion has again been repeated in 

 the present day by Majendie,* who, in sub- 

 sequently admittingf the existence of lympha- 

 tics in Birds, still contends against their being 

 the exclusive instruments of the function of 

 absorption. 



Traces of the lymphatic system in the pre- 

 sent class appear to have been observed by 

 SwammerdamJ as early as 1676, who sent 

 his preparation ' Lymphaticum peculiare ex ab- 

 domine Gallinae' to the Royal Society of Lon- 

 don; the lacteals were afterwards noticed in 

 the Stork by Jacobaeus in 1677, and traces 

 of lymphatics are described by Lang|| in 1704, 

 and by Martin Lister^" in 1711. Lymphatic 

 vessels and glands, however, considered as 

 such, according to the Hunterian doctrine of 

 absorption, were first undoubtedly seen by John 

 Hunter in the neck of a Swan, and the lac- 

 teals of Birds were afterwards re-discovered by 

 Hewson, who made the first attempt to give 

 a detailed account of the absorbent system in 

 Birds. Our knowledge of this system has 

 since been greatly enlarged by the labours 

 of Tiedemann,** Fohmann,ff Lauth,|J and 

 Panizza. 



* Journal dc Physiol. torn. i. p. 47. 



t Annales des Sciences Nat. iii. p. 410. 



i Birch, Hist, of the Royal Society, iii. p. 312. 



j Anat. Ciconiae in Acta Hafn. v. p. 247. 



|1 Physiologia Lips. fol. p. 99. 



T[ Dissertatio de Humoribus, 1711, 8vo. p. 228. 



** Anat. und Naturgeschichte der Vogel, torn. i. 

 p. 533. 



tf Anat. Untersuchungen liber die Vcrbindung 

 der Saugadern mit den Venon, 1821, p. 136. 



$$ Annales des Sciences Nat. iii. p. 381. 



Osscrvazionc Antropo-Zootomico Fisiologiciie, 

 fol. Pavia, 1830. 



