176 ANATOMY OF VERTEBRATES. 



Stork), which are often separated for a short extent, and con- 

 nected 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 situation appears 

 analogous to the ^ lobulus Spigelii ' of Mammalia. In the Com- 

 mon Fowl the left lobe is occasionally cleft from below so deeply 

 as to form two lobes on that side. In most species the right lobe 

 exceeds the left in size ; this is remarkably so in the Bustard, in 

 which the right lobe extends into the pelvis.^ In the Eagle, how- 

 ever, the left lobe is sometimes the largest. Each lobe is invested 

 by a double membranous tunic, one embracing it closely, the 

 other surrounding it loosely, like the pericardium of tlie heart. 

 They are formed by lamina? of the peritoneum, and by the air- 

 cells. The two adherent layers are continued from the base of 

 the liver, one over the anterior, the other over the posterior sur- 

 face, closely adhering to the proper capsule : the loose layers are 

 formed by the hepatic air-cell, surrounding each lateral lobe, the 

 thin border of which is usually free. 



The principal ligament of the liver is formed by a large and 

 strong duplicature of the peritoneum, which divides the abdomen 

 longitudinally like the thoracic mediastinum in Mammalia. It is 

 reflected from the linea alba and middle line of the sternum upon 

 the pericardium, 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 falciform ligament of Mammalia ; and, al- 

 though there is no free margin enclosing a round ligament, yet 

 the remains of the umbilical vein may be traced within the dupli- 

 cature of the membranes forming the septum. As the muscular 

 septum between the thorax and abdomen is wanting, there is con- 

 sequently no coronary ligament ; but the numerous membranous 

 processes which pass from the liver to the surrounding parts 

 amply compensate for its absence. 



The liver is of a lighter colour in Birds of flight than in the 

 heavier Waterfowl, where it is of a deep livid brown. Each 



^ The French Academicians (xl*. 2dc partie, pp. 99-109) saw this in some of their 

 Bustards : but in the male dissected by me the hepatic lubes were equal, and both 

 were long. 



