1438 



HUMAN ANATOMY. 



attached to the upper lateral wall, is formed by the fusion of the fascial lamellae con- 

 tributed by the sheaths of the levator palpebrae superioris and of the superior and 

 external straight muscles. Another and broader process, inserted along the median 

 wall, includes the blended extensions from the investments of the internal rectus and 

 superior oblique ; whilst a third process, formed by the union of prolongations from 

 the fasciae covering the inferior and internal recti and the inferior oblique, is attached 

 to the lower and median orbital wall. These fascial extensions, passing as they do 

 from the tendons of the eye-muscles to the orbital wall, restrain excessive muscular 

 action and hence the name, check ligaments, has been applied, especially to those 

 limiting the action of the internal and external recti. The processes also materially 

 assist in maintaining the position of the eyeball within the orbit. This function is 

 particularly exercised by the robust fascial expansion which stretches across the orbit 

 below the eyeball and as the suspensory ligament of Lockwood serves to support the 

 bulbus oculi. 



The orbital fat is prevented from projecting forward beyond a certain limit and, 

 therefore, from encroaching unduly upon the eyelid, by a sheet of fibrous tissue, the 



Fig. 1199. 



Upper tarsal plate 



Lachrymal gland 



Palpebral fascia, cut 

 Lateral palpebral ligament 



Palpebral fascia 



Lachrymal sac 



Median palpebral ligament 



Lachrymal punctiim and 

 canaliculus 



Nasal duct 



Opening of nasal duct in 

 inferior nasal meatus 



Lower tarsal plate 



Maxillary sinus 

 Dissection of orbit and adjacent structures, showing palpebral fascia, lachrymal sac and nasal duct. 



palpebral fascia or septum orbitale (Henle), which stretches across the orbital 

 entrance and materially strengthens and aids the eyelid in closing this aperture. 

 Above, the septum is attached to the border of the orbit, just behind the margin, 

 from which it extends downward to become firmly united ^\ith the common fascial 

 investment of the levator palpebrae superioris and superior rectus and, still lower, 

 with the upper convex border of the superior tarsal plate. On each side the septum 

 blends with the corresponding palpebral ligament, while below it passes from the 

 orbital margin to the inferior tarsal plate, after becoming united with the sheath 

 of the inferior rectus. The septum orbitale is not of uniform thickness, but is 

 strongest above, especially towards the sides, and weakest beneath the lower eyelid ; 

 further, in a general way, the sheet is more robust near its peripheral bony attach- 

 ment than where it joins the tarsal plates. In conjunction with the palpebral liga- 

 ments, it is so strong behind the angles of the eye that in these localities, particularly 

 medially, it is very unyielding and capable of resisting forward displacement. The 

 internal union of the levator palpebrse superioris with the septum orbitale enables 

 this muscle when it contracts to tense the fascial diaphragm. 



Practical Considerations. — The orbital cavity is somewhat pyramidal in 

 shape and its anterior or basal portion is occupied chiefly by the eyeball, which lies 

 slightly nearer the roof and the outer wall than the lower and inner walls. Its diameter 



