78 



THE SKELETOX 



wards and downwards in the anterior wall of the antrum; it conducts nerves to 

 the incisor and canine teeth. 



The outer wall is very oblique; it is formed by the orl)ital surface of the greater 

 wing of the splicnoid, and the malar. Between it and the roof, near the apex, is 

 the sphenoidal fissure, by means of which the third, fourth, ophthalmic division 

 of the tifth, and sixth nerves enter the orbit from the cranial cavity. The lower 

 margin of the fissure presents near the middle a small tubercle, from which One 

 head of the external rectus muscle arises. Between the outer wall and the floor, 

 near the apex, is the spheno-maxillary fissure, which alloAvs the second division of 

 the fifth nerve to enter the infraorbital groove from the spheno-maxillary fossa. 

 At the anterior margin of the fissure, the sphenoidal wing occasionally articulates 

 witli the maxilla, but frefjuently it is excluded by the malar. In front of the anterior 

 extremity of this fissure is the orbital orifice of the malar canal. Near the outer 

 extremity of the sphenoidal fissure a few^ small foramina may be seen, especially 

 in old skulls, which allow branches of the middle meningeal artery to creep into 

 the orbit. A vertical fissure, the spheno-malar, traverses the outer wall. It con- 

 tains the very small spheno-malar foramen, which allows the temporal branch of 



Fig. 86. — The Ixxer Wai.i. of the Orbit. 



FRONTAL SINUS 



NASAL PROCESS OF MAXILU 

 LACHRYMAL 



UCHRYMAL CANAL 



ORIFICE OF ANTRUM 



INFERIOR TURBINAL 



PALATE BONE 



ANTERIOR NASAL SPINE 



ANTERIOR ETHMOID CANAL 

 [•OSTERIOR ETHMOID CANAL 



OPTIC FORAMEN 



OS PLANUM OF ETHMOID 



^t- -fi+- SPHENO-PALATINE FORAMEN 

 -\— 4- VIDIAN CANAL, LEADING INTO THE 

 l>- SPHENO-MAXILLARY FOSSA 



SPHENOID 



EXTERNAL PTERYGOID PLATE 



— PALATE BONE 



the orbital nerve to escape from the orljit. This foramen is sometimes confined to 

 the malar Ixmc 



The inner wall, narrow and straight, is formed by the lachrymal, os planum 

 of the ethmoid, and a part of the body of the sphenoid. The ethmoid section of 

 the transverse suture contains the orifices of the anterior and posterior ethmoidal 

 canals: the former transmits the nasal nerve and anterior ethmoidal artery; the 

 latter the posterior ethmoidal artery, and a branch of the nasal nerve. 



Anteriorly is the lachrymal groove, and behind this the crest which gives origin 

 to the tensor tarsi. This wall has three vertical sutures: one between the nasal 

 process of the maxilla and the lachrymal, the ethmo-lachrymal, and one between 

 the OS planum and ])ody of the sphenoid. Occasionally the sphenoidal turbinal 

 bone appears in^ the orl)it between the os planum of the" ethmoid and the body of 

 the sphenoid (fig. 64). 



The orbit communicates with the cranial cavity })y the optic foramen and sphe- 

 noidal fissure; with the nasal fossa by means of the lachrvmal duct; with the zygo- 

 matic and spheno-maxillary fossffi "by way of the spheiio-maxillarv fissure. ^ In 

 addition to these large openings, the orbit has five other foramina— the infra-orbital, 

 malar, si)heno-malar, and the anterior and posterior ethmoidal canals — opening into 

 it or lea-ding from it. 



