COLUMBA. 363 
humerus. By this arrangement a contraction of the sub- 
clavian results in raising the wing. The tendon runs along 
beside the large coracoid bone, and on the outer side of this 
bone originates a small triangular muscle called the coraco- 
brachialis, the tendon of which is inserted in the head of the 
humerus. It apparently helps in depressing the wing. 
The large keel of the sternum is developed in response to 
the necessity for a large area of attachment for the ‘‘ flight- 
muscles.” In birds which do not fly the keel is absent. 
The sternum may now be removed by cutting round its 
edge posteriorly and laterally, and the abdominal cavity 
may be opened by a median ventral incision. 
The air-sacs should be noticed, large cavities with thin 
walls. They are nine in number, and communicate with 
the lungs (v.z.). Some are also produced into the interior 
of the bones, such as the humerus. Three pairs of them lie 
behind each other in a row on each side of the viscera, from 
which they are separated by an obiigue septum. 
Down the neck may be noticed two long tubes, one 
stiffened with bony rings, the ¢rachea, and the other soft, 
which is the esophagus. The trachea can be 
traced down to the thorax where it passes 
dorsal to the heart. The esophagus expands into a large 
thin-walled sac, the ¢vog, from which it passes into the 
body-cavity dorsal to the heart and terminates in a 
glandular stomach. The stomach opens directly into a 
large round gzzard with very thick muscular walls. The 
first loop of the small intestine is, as in other types, termed 
the duodenum, and in its loop there rests a whitish pancreas. 
The “ver is bilobed and lies over. the gizzard; it has swo 
bile-ducts. The left opens into the proximal loop of the 
duodenum and the right into the distal; the left is thick 
and short but the right is longer and more delicate. The 
pancreas has no less than three ducts which open into 
the distal loop of the duodenum. The rest of the smal 
intestine is coiled and of considerable length. It ends 
in a short rectum, and at the junction below the two 
is a pair of small pockets, the rectal ceca. The rectum 
opens into the cloaca. 
The alimentary system presents some peculiar characters. 
All modern birds like the pigeon have no teeth, though 
Alimentary. 
