GENERAL VIEW OF THE SKULL. 41 



orbital foramen in its centre. The zygomatic arch presents 

 externally a well-marked edge or line, which is continued 

 anteriorly by a ridge, called the maxillary spine. A process 

 thrown outwards and downwards by the frontal bone articulates 

 with the zygomatic arch about its middle ; it is called the frontal 

 or external orbital arch, and it indicates the division of the cavity 

 within into orbital and temporal fossag. 



The orbital fossa is a conical cavity, the oval entrance of which 

 is circumscribed by the frontal, the lachrymal, malar, and part of 

 the zygomatic process of the squamosal bone ; in addition to 

 these, the cavity is formed by the superior maxilla, the palatine, 

 -and the anterior wing of the sphenoid, called the orbito-sphenoid 



Fig. 12. 



Lateral aspect of a Horse's skull. 1, Occipital bone ; 2, Parieta 

 bone ; 3, Frontal bone ; 9, Nasal bone ; 11, Nasal peak : 10, Premaxilla 

 8, Superior maxilla ; 6, Laclirjmal bone ; 7, Malar bone ; 5, Zygomatic 

 process of the squamosal bone ; 4, Petrosal bone— c, its external 

 meatus ; 12, Inferior maxilla ; H. Coronoid process of inferior maxilla 

 occupying the temporal fossa ; K, Temporo-maxillary articulation ; 

 I, Molar teeth. 



l)one. Deep in the fossa anteriorly is a depression, the maxillary 

 hiatus, which leads to the palatine, spheno-palatine, and superior 

 dental foramina, and posteriorly another depression, the orbital 

 hiatus, containing the optic, pathetic, lacerated, and round 

 foramina. This cavity contains the eye, the muscles by which it 

 is moved, the lachrymal gland, and all accessories to the organ, 

 together with a large quantity of adipose tissue or fat. 



The temporal fossa is incompletely separated from the orbital 

 by the orbital arch, complete separation of these cavities by a 

 wall of bone being found only in man and the quadrumana. It 

 is oval in shape, situated in an oblique direction, from within 



