152 THE SKULL, [CHAP. 



and in this young skull still separated from the basisphenoid 

 in front by a vertical fissure. The basisphenoid (BS) is short 

 and deep, and has a strongly marked pituitary fossa or " sella 

 turcica " (sf] above. It has completely united with the pre- 

 sphenoid (PS\ though at birth the line of separation (below 

 the spot called the olivary process or tuberculum se/lce) is still 

 visible. In adult age large air-cells fill the interior of this con- 

 joined bone, which is the "body" of the so-called "sphenoid ' 

 of human anatomy. Anteriorly the presphenoid narrows to 

 a sharp vertical edge, which is in contact with the mesethmoid 

 (ME] above and the vomer ( Vo) below. The whole of the 

 upper part of the mesethmoid is ossified in the specimen 

 described, constituting the " lamina perpendicularis," but the 

 anterior and lower part forms the septal cartilage of the nose. 

 Its upper border forms a strong compressed triangular pro- 

 jection into the cranial cavity, called the " crista galli " (eg). 

 The posterior segment of the brain-case is completed, as 

 in the Dog, by the pair of exoccipitals (ExO), and a large 

 supraoccipital (SO). 1 The triangular upper part of the latter 

 may be considered to represent the interparietal, though it 

 very soon becomes incorporated with the rest of the supra- 

 occipital. The middle segment is completed by large ali- 

 sphenoids (AS), the "greater wings of the sphenoid bone," 

 and enormously extended, somewhat square- shaped parietals 

 (Pa) ; the frontal segment by narrow triangular orbito- 

 sphenoids (OS), the "lesser wings of the sphenoid bone," 

 and by large arched frontals (Fr). 



1 The "occipital bone" of human anatomy is formed by the coales- 

 cence of the basioccipital, exoccipitals, and supraoccipital. 



3 The "sphenoid bone" of human anatomy is formed by the union 

 of the basisphenoid, presphenoid, alisphenoids, orbitosphenoids, and 

 the pterygoids. The basal portion ultimately ankyloses with the 

 occipital. 



