COLUMBA. 361 
tongue. Immediately behind the tongue is a median slit, 
the glottis. Dorsally lie the two znternal nares, and behind 
them is a single Eustachian aperture which soon diverges 
into the two Eustachian canals to the ears. At the hind- 
end below the tail is a single median cloacal aperture. The 
fore-limbs are formed into wimgs and the hind-limbs form 
the gs. There are four toes terminating in claws. 
The whole body, with the exception of the beak and the 
lower part of the legs, is completely enveloped in a coat of 
eathers. A feather, structurally as well as 
ari oes i is an organ sud pei Nothing 
quite like it is found in any group outside the birds, 
A feather arises from the epidermis and remains attached 
to the skin by its base. If the feathers be plucked or 
pulled out of their epidermic pits, it is seen that they are 
attached only on certain areas of the skin called pzevyla, the 
portions of bare skin between them being called afferia. 
The skin itself is dry and powdery, and there is an 
absence of the numerous skin-glands found in the frog, with 
the exception of the large green-g/and at the base of the tail. 
This involves the “ preening” of the feathers by the bird, in 
which process the greasy secretion from the gland is spread 
by the bird’s beak over each feather. 
The largest feathers are found in the wing and tail and 
form the quill- or flightfeathers. The central axis of the 
feather is hollow in its lower part, called the gu¢//. Open- 
ing into the hollow cavity is a small aperture at the base, 
called the znferior umbilicus ; and at the distal end of the 
quill region is a smaller superior umbilicus.* Above the 
quill the axis is extended as the solid shaft, bearing on either 
side the vaze. The vane or flattened part is formed of a 
great number of parallel dards attached basally to the shaft 
and laterally to each other by small interlocking processes 
or barbules. 
The quills on the wing are called vemiges and those of 
tail are rectrices. A remex usually is more tapering, and has 
the vane very unequal in size in comparison with a rectrix, 
* This peculiar structure is explained by the development of the feather from a 
single tube, of which the part above the superior umbilicus splits longitudinally and 
spreads out to form the vane and shaft, leaving the quill to open to the exterior by 
the superior umbilicus. 
