THE EYE 317 



anteroventral angle of the orbit immediately medial to the zygomatic 

 arch and ventral to the anterior end of the infraorbital gland described 

 above. The gland is one of the salivary series, its duct passing down- 

 ward and opening through the mucous membrane of the cheek into the 

 cavity of the mouth. 



The application of the terms infraorbital and zygomatic to these 

 two glands is reversed by some authors. 



To examine the structure of the eye, the muscles of the eyeball 

 should be divided at their insertions, and the whole structure 

 should be removed. The second cranial or optic nerve (n. opticus) 

 is divided ; also the ophthalmic artery, a small branch of the internal 

 carotid which accompanies the nerve outward from the optic 

 foramen to the eyeball. 



The eye may be divided into medial and lateral hemispheres by 

 a circular incision, the lateral hemisphere, which contains the lens, 

 being again divided vertically. The parts should be examined 

 under water. The chief structures (Fig. 48, p. 92) comprise: 



(a) The fibrous tunic (tunica fibrosa oculi), the strong peri- 

 pheral coat enclosing the whole structure. It is divisible 

 into a medial portion, the sclera, or sclerotic coat, a thick 

 white investment of fibrous connective tissue enclosing the 

 greater part of the eyeball, and a smaller transparent lateral 

 portion, the cornea, covering the exposed surface. The 

 sclera is not so extensively exposed in the rabbit as it is in 

 man (white of the eye), a condition related to the very 

 small angle of movement in laterally placed eyes like those 

 of the rabbit. 



(b) The vascular tunic (tunica vasculosa oculi), the thin middle 

 coat of the eye; pigmented, except in albino animals. It 

 is divisible into: (1) a general portion, the chorioidea, 

 lying on the inner surface of the sclera ; (2) a muscular 

 portion, the ciliary body (corpus ciliare), composed of 

 numerous, radially arranged ciliary folds (plicae ciliares) 

 and forming an annular ridge about the periphery of the 

 lens; and (3) the iris, the latter forming a circular fold 

 suspended about the periphery of the lens and on its outer 

 surface. 



The ciliary body, which in man contains both radial and circular 

 muscle, has only the former in the rabbit. 



