44 TOPOGRAPHIC AND APPLIED ANATOMY. 



FIG. 16. A frontal section of the head through the orbital cavities and the maxillary sinuses (frozen section). 



anterior cranial fossa, the ethmoidal cells, the maxillary sinus, and the frontal sinus, furnish an 

 explanation for the fact that tumors growing from these adjoining regions may invade the orbit, 

 displace the eyeball, and endanger the orbital contents. 



The periosteum lining the orbit is known as the periorbUa. 



The eyelids are formed from cutaneous folds which grow over the protruding eyeball during 

 fetal life and become temporarily adherent along the line of the palpebral fissure. At this fissure 

 the skin is continuous with the mucous membrane lining the inner surface of the lid (palpebral 

 conjunctiva) which is reflected to the eyeball at the fornix to pass anteriorly to the corneal margin as 

 the ocular conjunctiva. Foreign bodies gaining access to the conjunctival sac occasionally become 

 firmly lodged in the conjunctival fornix. The orbicularis palpebrarum muscle lies immediately 

 beneath the skin, which possesses no subcutaneous fat. This muscle extends over the orbital 

 margin and consists of an orbicular portion, of a palpebral portion, and of a lachrymal portion 

 [the tensor tarsi Horner's muscle. ED.], the latter being a small bundle of fibers passing behind 

 the lachrymal sac. The eyelids receive a certain degree of solidity from the plates of connective 

 tissue of the so-called tarsal cartilages, which are better developed in the upper than in the lower 

 lids. In the upper lid this cartilage contains thirty to forty, in the lower lid, twenty to thirty 

 Meibomian glands, alveolar structures closely related to the sebaceous glands, which open at the 

 anterior margin of the lid and consequently upon the external cutaneous surface. They oc- 

 casionally lead to the formation of retention cysts and abscesses (stye, hordeolum). In front of 

 the orifices of these glands, at the margin of the lids, the cilia are arranged in two or three rows. 

 Their abnormal growth toward the eyeball leads to the disturbances of trichiasis and distichiasis. 

 The tarsal ligament or orbital septum [palpebral ligaments of English authors, who apply ihe 

 term " tarsal ligaments " to the bands which attach the inner and outer extremities of the 

 tarsal cartilage to the superior maxilla and malar bone respectively. ED.] is a dense lamina 

 of connective tissue extending in a frontal plane from the periosteum of the edge of the 

 orbit to the ciliary margin of the tarsal cartilage. It serves to close off the orbital cavity 

 from the eyelids and may offer a certain degree of resistance to the extension of inflam- 

 mations from within outward or in the opposite direction. This orbital septum is pierced 

 by the vessels and nerves passing from the orbit to the frontal region. 



When the lids are closed, the conjunctival sac is a slit-like space bounded by the palpebral 

 conjunctiva, the orbital conjunctiva, and the anterior surface of the cornea. It is deepest at the 

 middle of the eyelid, so that if the line of the fornix were projected upon the eyelid it would form 

 a circular line the diameter of which would extend from the external to the internal canthus. 

 The palpebral conjunctiva is more or less rich in leukocytes and small lymphatic nodules which 

 occasionally furnish the starting-point for trachoma. It is so firmly adherent to the tarsal plate 

 that there is no pathologic condition in which it is separated from this structure. This is in 

 marked contrast to the ocular conjunctiva, which is so loosely attached to the eyeball that it may 

 be pinched up into folds with the forceps ; it is easily separated from the eyeball by inflammations 

 and hemorrhages and occasionally overhangs the corneal margin. 



The lachrymal gland, situated in the lachrymal fossa of the frontal bone, consists of a larger 



