THE ORBITAL CAVITY. 



43 



[The bony roof of this canal is usually deficient behind. ED.] The external portion of the lower 

 wall is formed anteriorly by the orbital process of the malar bone ; the orbital process of the 

 palate bone also aids in forming the most posterior portion of the floor. 



The outer wall consists anteriorly of the orbital process of the malar bone, posteriorly of the 

 orbital surface of the great wing of the sphenoid, and above and anteriorly of the zygomatic 

 (external angular) process of the frontal bone. This surface presents the small temporomalar 

 canals for the temporal and malar branches of the orbital nerve. 



In addition to the optic foramen, which transmits the optic nerve and the ophthalmic artery, 

 another communication between the bony orbit and the cranial cavity is furnished by the 

 sphenoidal fissure (transmitting the oculomotor, the trochlear, the ophthalmic, and the 

 abducent nerves and the ophthalmic vein). The spheno-maxillary fissure (for the infraorbital 



Ethmoidal cells-.. 



Perpendicular 



plate of ethmoid 



bone 



Nasal cavity 



Vomer 



Inferior 

 turbinated bone 



Orbital plate of 

 frontal bone 



Crista galli 



Sphenoidal 



fissure 

 Great wing of 



sphenoid bone 

 Zygomatic pro- 

 cess of frontal 

 Optic foramen 



Sphenomaxillary 



fissure 

 - Infraorbital canal 



Maxillary sinus 



Alveolar process 



V 

 FIG. 15. A frontal section of the bony orbits of the nasal cavities and of the maxillary sinuses. 



vein) communicates in its anterior portion with the temporal fossa; the posterior portion is in 

 connection with the spheno-maxillary fossa. [In this fissure are found the infraorbital artery 

 as well as the vein, the superior maxillary division of the fifth nerve, the orbital branches of the 

 same nerve, and tw T igs from Meckel's ganglion. ED.] 



The external wall of the orbit is the strongest. The other walls are weaker and are conse- 

 quently thereby predisposed to perforation. 



Since the floor of the orbit is the roof of the maxillary sinus and the os planum in the inner 

 wall covers in the ethmoidal cells, it will be understood that when these walls are perforated, 

 the air from these accessory cavities may enter the orbit and cause emphysema and exophthalmos. 

 This may also be occasionally observed after perforation of the orbital roof, since the frontal 

 sinus frequently extends into the upper wall of the orbit, in rare cases as far as the optic foramen 

 (see Fig. 15). The relatively thin bony laminae separating the orbital cavities from the 



