170 



ANATOMY OF THE RABBIT 



wall, there is a shallow, horizontal groove, lodging in the natural 

 condition the temporalis muscle of the mandible, and therefore 

 representing a greatly reduced temporal fossa (fossa temporalis). 

 In the natural condition, the anterior portion of the groove is 

 converted into a foramen through the presence of a stout ligament 

 extending from the posterior supraorbital process to the base of 

 the zygomatic arch and through this foramen the external oph- 

 thalmic vein emerges from the orbit. The dorsal boundary of 



the fossa is formed by a 

 pronounced ridge, the tem- 

 poral line (linea temporalis), 

 the latter forming also the 

 lateral margin of the roof of 

 the skull in this region. 



Behind the posterior root 

 of the zygomatic arch, the 

 external surface of the lateral 

 wall is largely occupied by 

 the swollen tympanic bulla 

 (bulla tympani), formed by 

 the tympanic bone. It contains 

 the capacious tympanic cavity 

 (cavum tympani) and en- 

 closes the three small bones of 

 the middle ear, the auditory 

 ossicles (ossicula auditus), 

 the relations of which are 

 more fully dealt with below 

 (p. 188). The dorsal portion 

 of the tympanic bulla is con- 

 tinuous with a short bony 

 tube which opens at a short 

 distance dorsally by a large 

 oval aperture. This tube is 

 part of a more extensive 

 canal, the external acoustic 

 meatus (meatus acusticus 

 externus) which, in the natu- 



FlG. 

 frontal : 



Dorsal surface of the skull: F, 

 interparietal; L, lacrimal; M, 

 maxilla; MS, mastoid portion of petrosal 

 (petromastoid) ; N, nasal; P, parietal; SO, 

 supraoccipital (squamous portion of occipital) ; 

 SQ, squamosal; ZY, zygomatic. 



f.mx., maxillary fossa; f.t., temporal fossa; 

 l.n.s., superior nuchal line; l.t., temporal line; 

 p.f., frontal process of premaxilla; p.mx., 

 maxillary process of frontal; p.o.e., external 

 occipital protuberance; p.s.a. and p.s.p., anterior 

 and posterior supraorbital processes of frontal; 

 p.sc, subcutaneous process of lacrimal; p.z., 

 zygomatic process of squamosal; p.z.m., zygo- 

 matic process of maxilla; s.f., frontal spine; 

 s.m., spina masseterica. 



