parietal 



orbitosphenoid 

 frontal 



supraoccipital 



dermal petrosal 



squamosal 

 exoccipitol 



premaxilla 



basioccipitai 

 mastoid process 



occipital condyle 



foramen magnum 



dermal petrosal 



malleus incus 



stylomastoid foramen 



orbital fissure- 



orbitonasal foramen 



ethmoid foramen 



palatine foramina' 



foramen ovale 



petrosal 



occipital condyle 



mastoid process 



tympanic cavity 



exoccipitol 



|ugular foramen 

 temporal canal 



fenestra vestibuli 

 venous-facial canal 



Figure 3-9. Skull of Echidna (rachyglossus). A, lateral view; B, dorsal view; C, ventral view. 



choanal passage from just above the sphenopalatine foramen 

 to midway back on the ectopterygoid. Midway in their 

 length they are fused to the basipterygoid processes of the 

 basisphenoid and pierced by the pterygoid canal for the 

 palatine (Vidian) nerve. 



Separating the second quarter of the length of the nasal 

 passages (from front to rear) are the vomers. The two plates 

 are fused ventrally and diverge dorsally to enclose the ven- 



tral margin of the bony nasal septum (vertical plate of 

 ethmoid). The vomer extends from the anterior end of the 

 pterygoid to a point just behind the anterior end of the 

 palatine processes of the maxillae, where these meet at the 

 midline. 



The palatine extends up into the orbit to meet the frontal 

 and orbitosphenoid. This orbital extension is peculiar in that 

 it extends backward, overlapping the orbitosphenoid, so 



48 • OSTEOLOGY AND THE MAMMALIAN HEAD SKELETON 



