THE EAR 897 
The eyeball resembles that of the horse in shape, but is considerably smaller.* 
The sclera is often more or less pigmented; where non-pigmented, it may have 
a bluish tinge. The point of entrance of the optic nerve is about 2 mm. lateral 
to the vertical meridian, and about 7 mm. below the horizontal meridian.? The 
cornea is thicker than that of the horse. The tapetum of the chorioid is extensive 
at the outer side, but is a narrow strip medially. It has a metallic luster, shading 
from a brilliant green to a deep blue; centrally it has a reddish sheen. The iris is 
usually very dark colored. The granula form a continuous series of small nodules 
along the upper margin of the pupil and are most prominent centrally; they are 
very small on the lower margin. The optic papilla is much smaller and is not so 
sharply defined on ophthalmoscopic examination as that of the horse. Several 
relatively large retinal arteries radiate from the center of the papilla to the periphery 
of the retina. They may be seen to wind spirally around the veins, which are very 
large. The vitreous body is less fluid than that of the horse. 
The arteria centralis retine arises from a posterior ciliary artery and divides close to the 
optic papilla into three branches usually; the upper one is larger than the two lateral branches. 
The retina is more vascular than that of the horse; it has a round area centralis at the medial side, 
which is continued outward by a narrow strip of a similar histological structure. 
THE EAR 
The external ear is inclined outward. The middle part is much wider and less 
curved than in the horse. The apex is also wide and does not curve forward. 
The lower part of the anterior border is bent backward and bears long hairs. The 
posterior border is thin and is regularly convex, except below, where it is indented. 
The opening is wide and the concave surface presents four ridges; the convex 
surface presents corresponding depressions. The styloid process of the conchal 
cartilage is short and blunt. The edges of the annular cartilage are in contact at 
the medial side and the upper border is notched laterally. The scutiform cartilage 
is a very irregular quadrilateral plate; it is situated on the lateral aspect of the 
cranium, with its concave surface in contact with the fat and temporalis muscle. 
The osseous external acoustic meatus is directed practically straight inward; it is 
about twice as long as that of the horse, and tapers very gradually from without 
inward. The chief special characters of the auricular muscles are as follows: 
(1) The scutularis blends with the frontalis muscle. The interscutularis arises 
from the base of the processus cornus (or the corresponding area in polled cattle) 
and from the frontal crest. (2) The cervico-scutularis arises from the posterior 
surface of the cranium below the frontal eminence, and receives slips from the 
parieto-auricularis and cervico-auricularis superficialis. (3) The zygomatico- 
auricularis and scutulo-auricularis superficialis ventralis are fused. (4) The scutulo- 
auricularis superficialis dorsalis is distinct from the interscutularis; it arises from 
the superficial face of the scutiform cartilage. (5) The cervico-auricularis super- 
ficialis arises from the ligamentum nuche and ends on the convex surface of the 
conchal cartilage. (6) The parieto-auricularis arises from the nuchal surface of 
the frontal bone, the adjacent part of the parietal bone, and the ligamentum nuche; 
it is inserted below the preceding muscle. (7) The scutulo-auricularis superficialis 
accessorius arises from the superficial face of the scutiform cartilage and is inserted 
by a round tendon into the anterior part of the convex surface of the conchal car- 
tilage. (8) The cervico-auricularis profundus minor consists of two fasciculi: the 
medial, narrow part is deep red in color, and arises from the fascia of the cervical 
muscles lateral to the occipital attachment of the ligament nuchz; the lateral 
1 The average transverse diameter is about 42 mm., the vertical diameter, 41 mm., and the 
axis, 36mm. The angle between the optic axes is about 119°. 
2 The thickness of the sclera is about 2 mm. at the posterior pole, 1 mm. at the equator, and 
1.2 to 1.5 mm. near the cornea. 
57 
