ANATOMY OF THE HORSE. 
243 
THE SKIN covering the ear, although continuous with the 
other common integument of the body, exhibits within the cavity 
of the concha a comparatively thin and delicate texture. It 
becomes very thin and dry; and adheres to the cartilage by a 
cellular tissue, dense and compact, and destitute of adipose 
substance. After having lined the conchal cavity, it ends in a 
sort of blind pouch over the membrane of the tympanum, to 
which it contributes an outward layer. Underneath the skin we 
find numerous follicles, from which oozes a peculiar greasy mat¬ 
ter, for the purpose of keeping the parts soft and pliant. Below 
these follicles there is a second set of glands—the glandule 
ceruminoscc; whose ducts open between the roots of the hairs, 
and issue a sticky bitter matter, which, acquiring consistence 
from evaporation, constitutes the cerumen or wax of the ear. 
This secretion protects the bottom of the ear from the insinuation 
of insects, dust, &c. Sometimes it collects and forms concre¬ 
tions, obstructing the passage into the interior. 
Organization. —The arteries supplying the external ear are 
derived from the anterior and posterior auricular branches of the 
external carotid. Its veins return their blood into the jugular. 
Its nerves come from the portio dura of the seventh pair. 
Meatus Auditorius Ext emus. 
The external auditory canal is the tubular canal leading from 
the cavity of the concha to the membrane of the tympanum. Its 
commencement is dilated after the form of a funnel, from which 
the canal grows contracted, and at the farther end is elongated in 
the direction of the membrane of the tympanum. In composi¬ 
tion, it is partly osseous and partly cartilaginous: the auditory 
process of the petrous portion of the temporal bone constituting 
the inner, the annular cartilage the outer part. It is lined by 
an extension of the skin from the concha, and is plentifully fur¬ 
nished with sebaceous glands*. 
The Internal Ear. 
This comprehends two parts—the Tympanum and the Laby¬ 
rinth. 
Tympanum. 
The tympanum consists of an irregular cavity, situated within 
the petrous portion of the temporal bone, having the meatus au¬ 
ditorius externus on its outer side, the labyrinth on its inner. 
The cavity is lined by a very delicate mucous membrane, though 
* In the foetus a thick whitish substance is secreted by these glands, 
which answers the purpose of defending the parts against any acrimony in 
the liquor amnii. Alter birth, this secretion is discharged along with the 
subsequent issue of waxy matter. 
