ODONTOTORM 4—OIL-GLA ND 653 
ODONTOTORM A, see ODONTORNITHES. 
(ESOPHAGUS (Greek oicoddyos), so named by Aristotle, the 
gullet or “swallow” of plain English (cf DIGESTIVE SYSTEM, page 
136), the part of the alimentary canal from the LARYNX (page 
512) to the Sromacu. It passes down the right and dorsal side of 
the TRACHEA, with which and other adjoining parts it is connected 
by loose tissue, entering the thoracic cavity dorsally from the 
BRONCHI (page 58), and when not distended it forms numerous 
longitudinal folds owing to the yielding nature of the tunica mucosa 
(page 137). Deglutition is aided by simple mucous glands, but in 
many birds the middle portion of the Cisophagus forms a per- 
manent dilatation, the Crop (page 113), to the outer surface of 
which thin but broad bands of striped or voluntary muscle are 
generally attached. These may arise from the FURCULA (page 296) 
as in Pigeons, or from the skin of the neck as in the Gallinz, and 
their action assists the conveyance of the food from the crop to the 
stomach. During this process, especially if only little and dry food 
be left, Birds, Parrots for instance, may be occasionally observed to 
stretch their neck and gape widely with their mouth. 
OIL-BIRD, see GUACHARO. 
OIL-GLA ND (glandula uropygialis), in Birds the only cutaneous 
gland except some small organs in the external ear-passages. Con- 
sisting of two symmetrical portions, more or less united posteriorly 
in shape of a heart—since each half is broad and rounded in front 
and pointed behind—it is seated upon the levator muscles at the 
root of the tail. Internally it is formed of numerous secretory 
tubules which gradually unite in a common cavity opening on the 
surface through a variable number of orifices—there being from 3 to 
5 of them in many Water-birds, though only one to each half in 
Anseres—frequently prolonged in form of a nipple and occasionally 
united in a single tube, the double origin of which is, however, 
shewn by a median septum. In the Hoopoe alone, according to 
Nitzsch, there is but one orifice to the common cavity, wherein the 
stinking secretion of the gland, for which the female during incuba- 
tion and the young while they stay in the nest are notorious, is 
stored. The whole structure, which is surrounded by connective 
tissue and unstriped muscular fibres, is innervated by the first 
caudo-spinal nerves, and its blood-supply is in connexion with the 
caudal arteries and veins. 
In the majority of Birds this gland is well developed, being 
largest in those of aquatic habit, and especially in the TUBINARES 
and STEGANOPODES, as well as in Pandion (OSPREY) ; but it is also 
large in Steatornis (GUACHARO). It exists, though hardly in a 
functional condition, in certain PIGkONS (Ptilopus), Cacatua cristata 
(Cockatoo), and most Caprimulgi (NIGHTJAR), while in other 
