176 MANUAL OF ANIMAL BIOLOGY 



of the cranium. A pair of small irregular bones, the nasals, 

 form the dorsal wall of the olfactory capsules. On the ventral 

 surface of the olfactory capsules is a pair of small bones, the 

 vomers, which bear the vomerine teeth. The ventral wall of the 

 cranium is chiefly formed from a large unpaired, T-shaped bone, 

 the parasphenoid, the long stem of which extends anteriorly, and 

 the transverse portion posteriorly and to the sides, under each 

 of the auditory capsules. (W. f. 103.) 



The facial portion of the skull consists of the upper and the 

 lower jaws and the hyoid cartilage which with its bony processes 

 forms a plate-like structure in the ventral wall of the mouth cavity 

 where it supports the tongue. The hyoid apparatus in the 

 Frog is not so complete as it is in the Fishes where it forms the 

 elaborate gill-bearing visceral skeleton. (W. f. 103.) 



The bones of the upper jaw are immovably fastened to the 

 cranium. They consist of a pair of premaxillae bones which 

 form the extreme anterior portion of the upper jaw, a pair of 

 maxillae which are posterior to the premaxillae and form the 

 sides of the upper jaw, and a pair of quadratojugals which con- 

 stitute the posterior portion of the upper jaw. 



Each side of the lower jaw has as its basis a cartilaginous rod, 

 known as Meckel's cartilage. Anteriorly each rod is largely 

 covered by a dentary bone, and posteriorly by an angulosple- 

 nial bone. The jaws are attached to the cranium by a rather 

 complicated suspensory apparatus consisting of three bones on 

 each side, namely, the squamosal, pterygoid, and palatine. 

 (W. f. 103.) 



The Mammalian skull is considerably modified from that just 

 noted in the Frog. In the first place, the increase in the size of the 

 brain has necessitated an increase in size of the cranium as com- 

 pared with the facial region. This condition is seen in the most 

 marked degree in the skull of Man, as may be shown by a compari- 

 son of the cranial and facial portions of the skulls of Man and the 

 Gorilla. (W. f. 228.) 



There is also a great tendency toward a complete fusion of cer- 

 tain bones so that the adult skull comprises a smaller number of 

 separate bones than that of the embryo. Thus in early adult life 

 there are twenty- two bones in the human skull. This number is 

 considerably less than it was in earlier years and will be even more 

 reduced in old age. (W. f. 105.) 



