THE EAR 897 



The eyebaU resembles that of the horse in shape, but is considerably smaller.i 

 ihe 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 retinse arises from a posterior ciliary artery and divides close to the 

 optic papilla into three branches usuaUy; the upper one is larger than the two lateral branches. 

 Ihe retma 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 nuchae 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 nuchae; 

 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 nuchae; the lateral 



1 The average transverse diameter is about 42 mm., the vertical diameter, 41 mm., and the 

 axis, 36 mm. The angle between the optic axes is about 119°. 



2 The thickness of the sclera is about 2 mm. at the Dosterior pole, 1 mm. at the equator, and 

 1.2 to 1.5 mm. near the cornea. 



57 



