74 ATLAS AND TEXT-BOOK OF HUMAN ANATOMY. 



Fig. 95. — The left orbit seen from in front (-]-). 



Fig. 96. — The median wall of the left orbit, the outer wall having been removed (j). 



Fig. 97. — The outer wall of the right orbit, the median one having been removed (|). 



In all these figures the frontal bone is violet; the ethmoid orange; the lachrymal pink; the sphenoid green; the 

 nasal, parietal, and zygomatic bones white; and the palate bone blue. 



foramen. Its base is a quadrangle with rounded corners, and forms the entrance to the cavity 

 (aditiis orbita). 



The four walls of the orbit are designated the superior, the internal, the external, and the 

 inferior. Since there is no sharp dividing-line between the superior and internal and between 

 the internal and inferior walls, and also since such a dividing-line is partly absent between the 

 external and superior wall, the pyramidal orbital space possesses for the most part no sharp 

 angles; indeed, posteriorly the pyramid has practically but three sides. 



Each orbit is formed by seven bones: the frontal, the sphenoid, the ethmoid, the lachrymal, 

 the maxilla, the zygomatic, and the palatine. The sutures between these bones are described on 

 pages 79 and 80. The upper wall or the roof of the orbit (Fig. 95) is formed by the orbital 

 portion of the frontal bone, and in the posterior portion also by the lesser wing of the sphenoid 

 bone. It is horizontal, smooth, and slightly concave. 



The inner wall (Fig. 97) is formed anteriorly by the lachrymal bone and posteriorly by 

 the lamina papyracea of the ethmoid bone and by a small portion of the ala parva of the sphenoid 

 (near the junction of the inner wall with the roof). Below the lamina papyracea, the orbital 

 surface of the maxilla extends upward from the floor upon the inner wall, and its frontal process 

 also forms a narrow portion of the inner wall, internal to the lachrymal bone and immediately 

 adjacent to the internal orbital margin. The inner wall of the orbit is approximately vertical 

 and its anterior portion exhibits the fossa for the lachrymal sac. 



The floor of the orbit (Fig. 99) passes quite gradually into the inner wall, and its posterior 

 portion is separated from the largest (posterior) portion of the outer wall by the inferior orbital 

 (sphenomaxillary) fissure. Its greatest portion is formed by the orbital surface of the maxilla, 

 only a small posterior portion being formed by the orbital process of the palate bone. In the 

 anterior portion of the orbit the zygomatic bone also forms a narrow strip of the floor, but the 

 extent to which it takes part is subject to considerable variation (see page 71). The inferior 

 orbital wall is quite smooth and is almost exactly horizontal (slightly inclined outward, forward, 

 and downward). 



The outer wall of the orbit (Fig. 97) is the most isolated of all, since the two orbital fissures 

 separate from it the remaining walls in the posterior portion of the orbit. The inferior orbital 

 (sphenomaxillary) fissure separates more than half of the length of the outer wall from the floor, 

 and one-third of its extent is separated from the roof by the superior orbital (sphenoidal) fissure. 

 It is practically formed by two bones, the orbital surface of the greater wing of the sphenoid 

 bone contributing the posterior portion, and the orbital surface of the zygomatic bone the anterior 

 portion. The latter portion, however, also contains a part of the orbital portion of the frontal 

 bone, which extends downward more or less from the roof. The outer wall of the orbit is slightly 



