THE ORBITS 



109 



The following points ma}^ also be noticed: — 



The glabella, a smooth space between the converging superciliary arches. 

 The ophryon, the most anterior point of the metopic suture. 

 The nasion, the middle of the naso-frontal sutm-e. 



The subnasal point, the middle of the inferior border of the pjTiform aperture at the base 

 of the nasal spine. 



The alveolar point, the centre of the anterior margin of the upper alveolar arch. 



THE ORBITS 



The orbits [orbitae] (fig. 134) are two cavities of pyramidal shape, with their 

 bases directed forward and laterally and their apices backward and medially; 

 their medial walls are nearly parallel, but their lateral walls diverge so as to be 

 nearly at right angles to each other. Each cavity forms a socket for the ej'eball 

 and the muscles, nerves, and vessels associated vnth. it. 



Seven bones enter into formation of its w^alls, viz., the frontal, zygomatic, 

 sphenoid, ethmoid, lacrimal, palate, and maxilla; but as three of these — the 

 frontal, sphenoid, and ethmoid — are single median bones which form parts of 

 each cavity, there are only eleven bones represented in the two orbits. Each 

 orbit presents for examination four walls, a circumference or base, and an apex. 



The superior wall or roof, vaulted and smooth, is formed mainly by the orbital plate of the 

 frontal and is completed posteriorly by the small wing of the sphenoid. At the lateral angle 

 it presents the lacrimal fossa for the lacrimal gland, and at the medial angle a depression or a 

 spine for the pulley of the superior oblique muscle. 



Fig. 134. — The Medial Wall of the Orbit. 



Frontal sinus 



Nasal bone 



Frontal process of masiVLa.—-/^ 

 Lacrimal- — 



Lacrimal canal 



•Anterior ethmoid canal 



Posterior ethmoid canal 



Optic foramen 



Orifice of antrum 



Inferior nasal concha 



Palate bone 



Anterior nasal spine 



-Lamina papyracea of ethmoid 



_ 'f^Spheno-palatine foramen 



ft"' - 



—i^ Pterygoid canal, leading into the 

 pterygo-palatine fossa 

 Sphenoid 



External pterygoid plate 



The inferior wall or floor is directed upward and laterally and is not so large as the roof. 

 It is formed by the orbital plate of the maxilla, the orbital process of the zygomatic, and the 

 orbital process of the palate bone. At its medial angle it presents the naso-lacrimal canal, and 

 near this, a depression for the origin of the inferior oblique muscle. It is marked near the middle 

 by a furrow for the infra-orbital artery and the second division of the fifth nerve, terminating 

 anteriorly in the infra-orbital canal, through which the nerve and artery emerge on the face. 

 Near the commencement of the canal a narrow passage, the anterior alveolar canal, runs for- 

 ward and downward in the anterior wall of the antrum, transmitting nerves and vessels to the 

 incisor and canine teeth. 



The lateral wall, directed forward and medially, is formed by the orbital surface of the 

 great wing of the sphenoid, and the zygomatic. Between it and the roof, near the apex, is the 

 superior orbital (sphenoidal) fissure, by means of which the third, fourth, ophthalmic division 

 of the fifth, and sixth nerves enter the orbit from the cranial cavity; it also transmits some 

 filaments from the cavernous plexus of the sympathetic, the orbital branch of the middle men- 

 ingeal arterv, recurrent branches of the lacrimal artery, and an ophthalmic vein. The lower 

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

 the lateral rectus muscle arises. Between the lateral wall and the floor, near the apex, is the 

 inferior orbital (spheno-maxillarv) fissure, through which the second division of the fifth and 

 the infra-orbital vessels pass from the pterygo-palatine fossa to enter the infra-orbital groove. 

 At the anterior margin of the fissure the sphenoid occasionally articulates with the maxilla, but 



