The right lobe is larger than the left. In the hen of average size the liver weighs 35 grams. The parietal surface is convex and smooth. The surface which lies against the viscera is irregularly concave. The visceral surface furnishes exit for the bile duct and passage for the nerves and blood-vessels. This part is called the porta. The left lobe may be cleft from below so deeply as to form two lobes on that side. _Structure._—Each lobe is covered by a double serous membrane, one closely adherent, the other surrounding the structure loosely. These tunics, which are reflections of the peritoneum, are continued from the base of the liver, over both the anterior, and the posterior surface. The loose layer is formed by the air cells surrounding the lobes. The thin border of the liver is usually free. The two lobes of the liver are connected by a narrow isthmus of liver tissue. Occasionally there is a bird in which there occurs a _lobus Spigelii_ located at the posterior of the liver between the two principal lobes. The apex of the heart sacculates the diaphragm backward, so that part of this apex lies between the right and the left lobes (Fig. 43, No. 6 and 7). A ligament, the _falciform_, extends from the apex of the pericardial membrane, and attaching it rather firmly to the central connective tissue, or interlobar ligament. This ligament also has attachments to the inner surface of the sternum. The _broad ligament_ of the liver is formed posteriorly by a fold of the peritoneum. The _interlobar_, or _principal, ligament of the liver_ is formed by a large and strong duplicature of the peritoneum, which makes a longitudinal division in the abdominal cavity similar to the lateral division made by the thoracic mediastinum in mammals. It is reflected upon the pericardium from the linea alba and the middle line of the sternum, and passes deeply into the interspace of the lobes of the liver. It is attached to these lobes throughout their whole length and connects them below to one side of the gizzard. The lateral and posterior part of the liver attach to the adjacent air cells, and the whole viscus is thus kept fixed in its position during rapid and violent movements of the bird. The remains of the umbilical veins are traceable within the duplicature of the membranes forming the septum. These remains thus represent the round ligament of mammals. [Illustration: FIG. 38.—Cellular structure of liver, pancreas, and trachea. _A._ Liver. 1, Liver cells. 2, Sinusoid. 4, Nucleus of cells. _B._ Pancreas. 1, Island of Langerhans. 2, Alveolar cells. 3, Duct. _C._ Trachea. 1, Ciliated epithelia. 2, Glands. 3, Hyaline cartilage. _D._ Section of wall of ovum at Fig. 57 letter _d_. 1, Yolk. 2, Granular membrane. 3, Theca. 4, Blood-vessel. ]