20 VETEEINARY OPHTHALMOLOGY. 



eye and the muscles which move it. Some organs 

 accessory to the visual apparatus, such as the 

 lachrymal gland and the membrana nictatans, are also 

 contained in this cavity. The temporal fossa sur- 

 mounts the orbit and is incompletely separated from it 

 by the orbital arch (or process). Oval in shape, lying 

 obliquely from above to below, and from within out- 

 wards, on the sides of the cranium, the temporal fossa 

 is limited, within by the parietal ridge, and outwardly 

 by the anterior border of the longitudinal root of 

 the zygomatic process. It lodges the temporal 

 muscle. 



The orbital cavity is situated at the side of the 

 head at the point corresponding to the union of the 

 cranium and the face. It is lined by a fibrous mem- 

 brane, designated the ocular sheath (ocular membrane 

 or periorbita), which is attached posteriorly to the bor- 

 der of the orbital hiatus and anteriorly to the upper 

 lip of the orbit, being prolonged beyond the exteinal 

 lip of this osseous rim to form the fibrous mem- 

 brane of the eyelids. Strong externally, the ocular 

 sheath is thin within the cavity, composed of elastic 

 and inelastic fibers (unstriped muscular fibers have 

 also been included in its composition), traversed by 

 vessels and nerves. Thus completed, the orbital cavity 

 lias the form of a regular hollow cone, open at its base, 



man and the quadrumana has the orbital cavity complete bony 

 walls. 



