THE ENDOSKELETON 



695 



The sphenoids are: 



The basisphenoid, extending forward to the sella turcica. 

 The presphenoid, extending from the trabeculae to the ethmoid 

 plate. 



The alisphenoid, closely related to the basisphenoid. 



The orbitosphenoid, in close relation with the presphenoid. 



Fig. 414. 



A,' A ventral view of the skull of a rabbit, ol., External process of the 

 alisphenoid ; b.oc., basioccipital ; b.ap., basisphenoid ; e.a.m., external auditory 

 meatus ; ex.oc., exoccipital ; f.m., foramen magnum ; inc., incisors ; ju., jugal ; mr., 

 molars ; m.x., maxilla ; oc., occipital condyle ; pi., palatine ; pm., premaxilla ; 

 pmr., premolars; pr.sp., presphenoid; pt., pterygoid ; s.oc., supraoccipital ; ty.b., 

 tympanic bulla ; v, vomer ; zy.mx., zygomatic process of maxilla ; zy.s., zygomatic 

 process of squamosal. (From Borradaile.) 



B, A side view of a rabbit's skull. Pmx., Premaxilla ; No., nasal ; Fr., frontal ; 

 Pa., parietal ; Sq., squamosal ; S.O., supraoccipital ; Per., periotic ; T., tympanic 

 (the reference line points to the bony external auditory meatus, beneath it lies 

 the inflated bulla) ; PO., paroccipital process. (From Thomson.) 



The ethmoids are divided as follows : 



Mesethmoid, lying medially. 



Ectethmoid, one on each side of the mesethmoid. 



The ectethmoid becomes the ectethmoid labyrinth which comes to 

 lie between ectethmoid and mesethmoid, and the turbinate bones are. 

 sometimes added here. 



From the otic capsule are developed various otic or petrosal bones. 



These are usually divided into: 



Prootic, lying in front of the ear. 



Opisthotic, lying behind, although usually meeting below with a 



