THE ORBITAL CAVITY. 45 



superior portion and of a smaller inferior portion, the latter not always being sharply denned. 

 The convex surface of the gland is in relation with the fossa, and the anterior border of the gland 

 extends to the supraorbital margin, so that it may be readily exposed above the external canthus 

 by an incision along the supraorbital margin dividing the skin, the orbicularis palpebrarum 

 muscle, and the tarsal ligament. The lachrymal gland may also be reached through the fornix 

 conjunctivas without making a cutaneous incision. The lachrymal ducts, about ten in number, 

 empty into the fornix above the external canthus of the eye. The two lachrymal canals, the in- 

 ferior being somewhat broader and shorter than the superior, are about 0.5 millimeter in diameter, 

 but they are so elastic that they may be dilated with sounds to three times this diameter. They 

 commence at the inner ends of the palpebral margins in the puncta lachrymalia, which the reader 

 may easily see in his own eye with the aid of a mirror. These puncta are situated at the summit 

 of small elevations known as the lachrymal papillas. They dip into the lacus lachrymalis and 

 take the tears from this situation to the lachrymal sac, which is lodged in a deep groove formed 

 by the lachrymal bone and the nasal process of the superior maxillary. The upper portion of the 

 lachrymal sac is in intimate relation with the lower end of the frontal sinus, thus explaining the 

 occasional occurrence of purulent dacryocystitis in purulent inflammations of the frontal sinus. 

 The nasal duct, a direct continuation of the lachrymal sac, runs downward in a canal of the 

 same name to empty into the inferior meatus of the nose. The direction of this duct is not 

 directly downward, but somewhat inward and backward, being subject to slight variation. 



The most important part of the orbital contents, the eyeball, does not completely fill the orbital 

 cavity. It lies in the anterior broad portion of the orbit in such a way that when the individual 

 looks straight ahead, the center of the cornea is in a vertical line connecting the middle points of 

 the upper and lower orbital margins. The optic nerve, entering at the optic foramen, runs ap- 

 proximately in the long axis of the orbit to the posterior surface of the eyeball, which it reaches 

 some millimeters to the nasal side of the posterior pole. During this course, the nerve, surrounded 

 by a sheath of dura and pia mater, does not run in a straight line, but in certain slight curves which 

 vary even in carefully made sections. These small curves are probably not of much importance 

 to the physician, but they may be important to the physiologist. With good fortune, a horizontal 

 frozen section may strike both nerves in the same plane and show their entire course (Fig. 17). 



The space between the eyeball, the optic nerve, and the periorbita is filled by the orbital fat, 

 the voluntary muscles of the eye, the blood-vessels, and the nerves. 



The orbital fat is separated from the eyeball by the capsule of Tenon, forming a socket in 

 which the motions of the eyeball take place. Between the capsule and the bulbus oculi there 

 is a capillary lymphatic space, the spatium interjasciale (Tenoni) or space o] Tenon. In the 

 vicinity of the cornea the capsule of Tenon gradually disappears in the connective tissue overlying 

 the sclerotic coat. The ocular muscles must consequently perforate this capsule of Tenon before 

 they become inserted into the sclerotic coat ; the same is true of the vessels and nerves which enter 

 the eyeball behind the equator. [To reach the insertions of the muscles into the sclerotic it is 

 therefore necessary to cut two layers, the ocular conjunctiva and the capsule of Tenon. ED.] 



All of the muscles 0} the eye (see Figs. 16 and 17), with the exception of the inferior oblique, 

 arise from the circumference of the optic foramen. As they pass forward they form a partly 

 open hollow pyramid, the base of which is situated at about the equator of the eyeball. The 



