ON SOME FOSSIL REMAINS OF MAN 323 



fles, and becomes soldered into one piece long before the 

 roof. I conceive then that the base of the skull may be 

 demonstrated developmentally to be its relatively fixed 

 part, the roof and sides being relatively moveable. 



The same truth is exemplified by the study of the 

 modifications which the skull undergoes in ascending 

 from the lower animals up to man. 



In such a mammal as a Beaver (Fig. 28), a line (a. b.) 

 drawn through the bones, termed basioccipital, basi- 

 sphenoid, and presphenoid, is very long in proportion to 

 the extreme length of the cavity which contains the cerebral 

 hemispheres (g. 7i.). The plane of the occipital foramen 

 (b. c.) forms a slightly acute angle with this ' basicranial 

 axis/ while the plane of the tentorium (i. T.) is inclined 

 at rather more than 90 to the ' basicranial axis ' ; and 

 so is the plane of the perforated plate (a. c?.), by which 

 the filaments of the olfactory nerve leave the skull. Again, 

 a line drawn through the axis of the face, between the 

 bones called ethmoid and vomer the " basifacial axis " 

 (/. e.) forms an exceedingly obtuse angle, where, when 

 produced, it cuts the ' basicranial axis.' 



If the angle made by the line b. c. with a. b. t be called 

 the ' occipital angle/ and the angle made by the line a. d. 

 with a. b. be termed the ' olfactory angle/ and that made 

 by z. T. with a. b. the ' tentorial angle/ then all these, in 

 the mammal in question, are nearly right angles, varying 

 between 80 and 110. The angle e. /. b., or that made 

 by the cranial with the facial axis, and which may be 

 termed the ' cranio-facial angle/ is extremely obtuse, 

 amounting, in the case of the Beaver, to at least 150. 



But if a series of sections of mammalian skulls, inter- 

 mediate between a Rodent and a Man (Fig. 28), be ex- 

 amined, it will be found that in the higher crania the 

 basicranial axis becomes shorter relatively to the cerebral 

 length ; that the ' olfactory angle ' and ' occipital angle ' 

 become more obtuse ; and that the ' cranio-facial angle ' 

 becomes more acute by the bending down, as it were, of 

 the facial axis upon the cranial axis. At the same time, 

 the roof of the cranium becomes more and more arched, 

 to allow of the increasing height of the cerebral hemi- 

 spheres, which is eminently characteristic of man, as well 

 as of that backward extension, beyond the cerebellum, 

 which reaches its maximum in the South America 

 Monkeys. So that, at last, in the human skull (Fig. 29), 



