The Head and Neck. 167 



(a) The levator palpebrae superioris. Origin : Wall of the orbit 



above the optic foramen. Insertion: Upper eyelid. 



This thin sheet of muscle should be separated from the underlying 

 rectus superior of the eyeball. 



(b) The obliquus superior. Origin : Anterior margin of the optic 

 foramen. The muscle passes upward on the wall of the orbit, 

 then beneath a fibrous cord, the trochlea, which bridges a 

 small portion of the orbital wall and changes the course of 

 the tendon by a considerable angle. Insertion: Antero- 

 dorsal portion of the eyeball. 



(c) The obliquus inferior. Origin: Lacrimal bone. Insertion: 

 Posteroventral portion of the eyeball. 



(d) The four recti muscles, superior, inferior, medialis, and 

 lateralis, arise from the boundary of the optic foramen, and 

 are inserted respectively on the dorsal, ventral, anterior, and 

 posterior portions of the periphery of the eyeball. 



(e) The retractor bulbi (best seen after the removal of the eye) 

 arises in common with the foregoing recti muscles, and is 

 inserted on the medial portion of the eyeball around the 

 optic nerve. It consists of four distinct parts. 



(f) The Harderian gland (gl. Harderiana) is a large compact gland 

 lying in the anterior portion of the orbit. It is composed of 

 two portions, one of which is greyish red, the other white. 

 The duct opens on the inner surface of the third eyelid. 



(g) The lacrimal gland (gl. lacrimalis) is a much smaller, also 

 darker, structure lying close to the skull in the temporal angle 

 of the orbit. It communicates by several fine ducts with the 

 inner surface of the upper eyelid. 



The infraorbital gland (gl. infraorbitalis) is a diffuse white or 

 yellowish gland lying in the anteroventral angle of the orbit immedi- 

 ately medial to the zygomatic arch. The gland is one of the salivary 

 series, its duct .passing downward and opening through the mucous 

 membrane of the cheek into the cavity of the mouth. 



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

 be divided at their insertions, and the whole structure 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 by a circular incision into medial and lateral 

 hemispheres, the lateral hemisphere, containing the lens, being again 

 divided vertically. The parts should be examined under water. The 

 chief structures (Fig. 50) comprise : 



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

 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. 



