486 



MAMMALIA. 



well-marked process on each side, the paroccipital or 'jugular 

 (paramastoid) processes (Pm). The base of the skull is well ossi- 

 fied in cartilage bone. The basisphenoid (Spb) usually remains 

 distinct from the presphenoid (Ps) for a considerable time/- Its 

 upper surface is hollowed out as the pituitary fossa (sella lurcica} 

 which lodges the pituitary body. The alisphenoid (Als) and 

 parietals (Pa) complete the basisphenoid section of the skull and 

 the orbitosphenoid and frontals (Ors, Fr) the presphenoid region. 

 There is no interorbital septum, and the ethmoid with its per- 

 forated or cribriform plate (lamina cribrosa) constitutes the 

 anterior boundary of the cranial cavity. In the Primates only 



01 



FIG. 259. Skull of a goat, from the side (from ClausK C occipital condyle, .Fo'optic 

 foramen, Fr frontal," Jmx premaxilla, Ju jugal, La lacrymal, MX maxilla, Na nasal, 

 01 exoccipital, Os supraoccipital. Pa parietal, Pal palatine, Pe mastoid portion of 

 petrosal, Pm paroccipital process, Pt pterygoid, Sq sciuamosal, Ty tympanic. 



do the lateral parts of the ethmoid (lamina papyracea) take part 

 in forming the inner wall of the orbit. In all other cases the 

 ethmoid is placed in front of the orbit and its lateral portion 

 (os planum) is covered by the maxillae. Two parts may be dis- 

 tinguished in the ethmoid, (1) a median plate (lamina per- 

 pendicularis) which is continued in front into the cartilaginous 

 nasal septum and is underlaid by the vomer and covered dor- 

 sally by the nasals, (2) the lateral masses. The lateral masses 

 of the ethmoid, or spongy bones as they are called, result from 

 the ossification of the complexly folded cartilage of the nasal 

 capsule, over the surface of which the terminal .fibres of the 



