532 ZOOLOGY. 
Between the liver and the glandular stomach lies the 
small, somewhat elongated, reddish brown spleen. 
In birds, as in most vertebrates, several spinal nerves unite 
to form a brachial plexus, part of which is shown at B, and 
which supplies the wings. Posteriorly, there is also formed 
a plexus, the lumbar, for the legs. 
The muscles of the limbs are much modified in accordance 
with the peculiar locomotion of birds. In connection with 
the power of flight, the sternum has a very large keel, to 
which are attached the pectoral muscles. The pectoralis 
major (Pe) is the most external ; it arises from the outer 
half of the keel and is inserted into the humerus, and effects 
the downward stroke of the wing. The second pectoral 
(pectoralis tertius of some authors and the homologue of 
the comparatively insignificant subclavius of human anat- 
omy) arises from the inner portion of the keel, runs forward- 
and outward, and, tapering off, passes through a groove be- 
tween the coracoid and sternum, as over a pulley, to be in- 
serted into the humerus. The wing is raised by its action. 
In the ostrich, etc. (Ratite), the breast-bone has no keel, 
and the disposition of the muscles of the rudimentary wings 
‘ therefore differs greatly from that here described. (Minot.) 
The ovary may be distinguished by the large incipient eggs 
forming the greater part of the mass. The right ovary is 
usually undeveloped, but when partly formed, as in some 
hawks, the eggs do not mature. 
The “‘ white’ is deposited around the true egg in the upper 
part of the oviduct, while the shell is secreted from glands 
emptying into the lower part of the duct. The eggs of 
birds are enormous in proportion to those of other verte- 
brate animals, except the lizards. The egg of the Hpyornis, 
an extinct bird of Madagascar, is about a third-of a metre 
(13% inches) in length, and as the egg is in reality a cell, 
this is the largest cell known. The development of the 
chick is better known than that of any other animal. It 
travels the same, developmental path as other vertebrates in 
which an amnion and allantois are formed. About the sixth 
day of embryonic life the bird-characters begin to appear, 
the wings berin to differ from the legs, the crop and giz- 
