CHAP. V] THE CRANIA OF THE SIMIIDAE (PRIMATES) 227 



be connected by an osseous bar with the posterior process of that 

 name. (The invasion of the floor or base of the anterior fossa by 

 the frontal bone may be recalled here as distinguishing the African 

 Simiidae from the Orang-utan and from Man.) The orbital roof 

 is much steeper than in Man for it is still comparatively free from 

 the displacement due to an actively-growing brain. The basis 

 cranii includes the ethmoid, sphenoid, and occipital elements, but 

 a crista galli does not exist in the Simiidae as a rule, and is absent 

 from the specimens shewn in the illustrations. Anteriorly, the nasal 

 spine of the frontal bone will be seen to be rudimentary, and in 

 the Orang-utan the superior maxilla may come into the section in 

 place of the nasal bone, as a consequence of the diminutive size, 

 or extent, or of the absence of the latter element. But it is to the 

 arrangement of the ethmoid, sphenoid and basi-occipital elements 

 of the cranial base that special attention must be given. 



It will be seen (cf. Figs. 149 and 150 b) that anteriorly the line of 

 section of the upper margin of the ethmoid forms a plateau, nearly 

 horizontal in direction, and that passing backwards from this, the 

 line of the upper margin of the sphenoid is (with the exception of 

 a hillock representing the section of that portion of the presphenoid 

 which lies between the two orbito-sphenoids) practically continuous 

 with the clivus, the line passing almost directly to the margin of 

 the foramen magnum without interruption. The point to which 

 attention is drawn is that this line forms with that of the upper 

 margin of the ethmoid an angle salient endocranially, open below, 

 and moreover widely open, approximating to the value of 180°, or 

 t\v( i right angles. A glance at the human skull (cf. Fig. 150 a) shews 

 the inclination of the two lines to be represented by a very much 

 smaller angle. There are various ways of measuring this angle, 

 and these will be described in detail in another connection, but 

 for the moment it will suffice to call attention to the general 

 appearance. The conclusion is, that in the simian skull the 

 basal elements are arranged nearly in line, but that in the human 

 skull this line is inflected ; this inflection constitutes an important 

 peculiarity of the human skull. 



If we pass beyond the limits of this group of animals and 

 turn our attention first to the lower Primates, and secondly to 

 other mammals, we shall find that the straightness of the series 



15—2 



