in.] THE CRANIAL SKELETON. 135 



be plainly visible, instead of being hidden, as it is in man. 

 The five foramina of that fossa, viz. the rotundum, vidian, 

 pterygo-palatine, posterior palatine, and spheno-palatine, are 

 generally present in the Mammalian class, but with the open- 

 ing out of the fossa become more or less, and in different 

 degrees, separated from each other as compared with their 

 common juxtaposition in man. The spheno-palatine and 

 posterior palatine foramina may together be represented by a 

 single small opening, as in the Ornithorhynchus. 



35. Before considering the INTERNAL SURFACE of the 

 cranium as treated of in Anthropotomy, it may be well to 

 note the relations and conditions presented by a vertical 

 longitudinal section of the entire skull, which are exceedingly 

 significant and instructive. 



The basi-cranial axis of man forms an angle which approxi- 

 mates to a right angle with the basi-facial axis. 



In Birds the angle may be as marked as in man, and the 

 human condition may be even much surpassed, as in the Wood- 

 cock, where the facial part is so extremely bent down that its 

 axis forms a very acute angle with the basi-cranial axis. 



Now, in all the lowest Vertebrates these two axes are in one 

 straight line, as in Fishes, Batrachians, and most Reptiles ; 

 and even in most Mammals the angle formed by them is 

 an exceedingly open one, approximating to 180. 



The importance,, however, of this distinction is not really 

 so great as at first appears, for there are great differences 

 with regard to it between animals which are very nearly 

 allied. Thus the adult Chacma Baboon differs from his ally 

 the Mandrill in this respect almost as much as man differs 

 from the Gorilla ; and while the Deer has the two axes almost 

 on a line, in the Sheep and Ox they form a very marked angle. 



The shortness of the basi-cranial axis in man when com- 

 pared with the extreme length of the true brain cavity, is a 

 much more distinctive feature, as in all lower forms this axis is 

 very much longer. Thus, in the Sheep, the basi-cranial axis is 

 as long as the entire cerebral cavity, and in the lowest Verte- 

 brates (where the cerebral hemispheres form but a small part 

 of the brain) it very greatly exceeds it. 



Similarly the angle formed by it with the plane of the occi- 

 pital foramen, which is so very open in man, contracts in lower 

 Vertebrates till it becomes a right angle ; and the same may 

 be said as to the olfactory angle, or that formed with the 

 basi-cranial axis by the plane of the cribriform plate, or 

 its morphological equivalent. 



