I30 THE SKULL. [chap. 



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

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

 turcica " {si) above. It has completely united with the pre- 

 sphenoid {PS), though at birth the line of separation (below 

 the spot called the olivary pi'oass or tiiho culiiin sdke) 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)} 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). 



Of the fossjE into which the cranial cavity is divided, the 

 olfactory fossa is very small, rather narrow, elongated, and 



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

 cence of the basioccipital, exoccipitals, and supraoccipital. 



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

 of the basisphenoid, presphenoid, ahsphenoids, orbitosphenoids, and the 

 pterygoids. The basal portion ultimately ankyloses with the occipital. 



