326 



AVES. 



it bears a proportion of one-tenth, in some of 

 the latter of one-tvventy-ninth part of the entire 

 body. 



The liver (m m, jig. 163, 165) is situated 

 a little above the middle of the thoracic-abdo- 

 minal cavity, with its convex surface towards 

 the abdominal parietes,and its concavity turned 

 towards the subjacent viscera : the right lobe 

 covers the duodenum, pancreas, and part of the 

 small intestines ; the left lobe covers the pro- 

 ventriculus and part of the gizzard; and the 

 apex of the heart is received between the upper 

 ends of these principal lobes. The liver is, as 

 it were, moulded upon all these parts, and pre- 

 sents corresponding depressions where it comes 

 in contact with them. 



It is generally divided into two nearly 

 equal lobes, which are often separated for 

 a short extent, and connected together by a 

 narrow isthmus of the glandular substance. 

 In some birds, however, as in the Pigeon, 

 Cormorant, Swan, and Goose, there is a third, 

 smaller lobe, situated at the back of the liver 

 between the lateral lobes, which from its situ- 

 ation appears analogous to the lobulus Spigelii 

 of Mammalia. In the Common Fowl the left 

 lobe is occasionally cleft so deeply as to form 

 two lobes on that side. In some species the 

 right lobe exceeds the left in size ; this is most 

 remarkable in the Bustard, in which the right 

 lobe extends into the pelvis. In the Eagle, 

 however, the left lobe has been observed to be 

 the largest. Each lobe is invested by a double 

 membranous tunic, one embracing it closely, 

 the other surrounding it loosely, like the peri- 

 cardium of the heart. They are formed by 

 laminae of the peritoneum, which seems to 

 split at the exterior thin edge of the liver into 

 four layers, two being continued upon the 

 anterior and posterior surfaces adhering to them, 

 the other two forming the loose exterior cap- 

 sule. 



The principal ligament of the liver is formed 

 by a large and strong duplicature of the peri- 

 toneum, which divides the abdomen longitu- 

 dinally like the thoracic mediastinum in Mam- 

 malia. It is reflected from the liriea alba and 

 middle line of the sternum upon the pericar- 

 dium, and passes deeply into the interspace of 

 the lobes of the liver ; it is attached to these 

 lobes through their whole extent, and connects 

 them.below to the gizzard on one side and to the 

 duodenal fold on the other: the lateral and 

 posterior parts of the liver are attached to the 

 contiguous air-cells ; and the whole viscus is 

 thus kept steady in its situation during the 

 rapid and violent movements of the bird. The 

 ligament first described is analogous to the fal- 

 ciform ligament of Mammalia; and, although 

 there is no free margin inclosing a round liga- 

 ment, yet the remains of the umbilical vein 

 may be traced within the duplicature of the 

 membranes forming the septum. As the mus- 

 cular septum between the thorax and abdomen 

 is wanting, there is consequently no coronary 

 ligament; but the numerous membranous pro- 

 cesses which pass from the liver to the sur- 

 rounding parts amply compensate for its ab- 

 sence. 



The liver is of a lighter colour in Birds of 

 flight than in the heavier Water-fowl. Each 

 lobe has its hepatic artery and vena portae. 

 The hepatic arteries are proportionally small, 

 but the portal veins are of great size, being 

 formed not only by the veins of the intestinal 

 canal, pancreas, and spleen, but also by the 

 inferior emulgent and sacral veins. The blood, 

 which has circulated in the liver, is returned 

 to the inferior cava by two venae hepaticoe. 

 There are occasionally some smaller hepatic 

 veins in addition to the two principal ones. 

 The coats of the portal and hepatic veins ap- 

 pear to be equally attached to the substance 

 of the liver. 



The biliary secretion is carried out of the liver 

 by two and sometimes three ducts ; one of these 

 terminates directly in the intestine, and is a 'he- 

 patic duct ' (w, n,Jig. 165); the other enters the 

 gall-bladder, and is a ' cyst-hepatic duct ' (o',Ji-g. 

 1 65) ; the cystic bile is conveyed to the duo- 

 denum by a < cystic duct ' (o,fig 165). Where, 

 as in a few instances, the gall-bladder does not 

 exist, both hepatic ducts terminate separately 

 in the duodenum (n, n, Jig. 163); but in no 

 case is there a single ductus communis cho- 

 ledochus as in Mammalia. 



The gall-bladder (p, Jig. 165) is situated 

 near the mesial edge of the concave or under 

 side of the right lobe, and is commonly lodged 

 in a shallow depression of the liver; but some- 

 times, as in the Eagle, Bustard, and Cormorant, 

 only a very small part of the bag is attached to the 

 liver. It has the same structure as in Mamma- 

 lia, manifesting no visible muscular tunic, and 

 having its inner surface delicately reticulated. 



The gall-bladder is present in all the Rap- 

 tores, Insessores, and Natatores. It is want- 

 ing in a great proportion of the Scansores, as 

 in the Genus Rhamphastos and in the whole 

 of the Psittacida and Cuculida. Among the 

 Rasores the gall-bladder is constantly deficient 

 in the Columbidte. or Dove-tribe alone, in which 

 the coeca are shorter than in any other vege- 

 table feeder: (n n, jig. 163, are the two he- 

 patic ducts terminating apart from one another 

 in the Pigeon.) The gall-bladder is occasion- 

 ally absent, according to the French Acade- 

 micians, in the Guinea-fowl; and they also 

 found it wanting in two out of six Demoi- 

 selles ( Anthropoides Virgo). The gall-blad- 

 der is small and sometimes absent in the 

 Bittern : it is always wanting in the Ostrich. 



The bile, as before observed, passes directly 

 into the gall-bladder, and not by regurgitation 

 from a ductus choledochus ; the cyst-hepatic 

 duct arises from the right lobe, and is con- 

 tinued in some birds along that side of the 

 bag which is in contact with the liver, where it 

 penetrates the coats of the cyst and terminates 

 about one-third from the lower or posterior end. 

 In the Horn-bill we found it passing over the 

 upper end of the bladder to the anterior or free 

 surface, and the cystic duct continued from 

 the point where the cyst-hepatic duct opened 

 into the bladder; so that the cystic duct had 

 a communicaton both with the reservoir and 

 the cyst-hepatic duct; being somewhat ana- 

 logous to the ductus communis choledochus; 



