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 tubercuhim 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," 2 

 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. 



2 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. 



