8 ELEMENTARY BIOLOGY. [CHAP. 



3 . The base of the skull. 



a. Running along the greater part of the floor of 

 the cranial cavity, from the occipital foramen 

 to the vomers, is a bone shaped like a dagger 

 with a short handle and a strong guard. The 

 latter spreads out under the pro-otics. This is 

 the parasphenoid bone. 



b. Appearing at the base of the skull, at the front 

 end of tf c parasphenoid, is the girdle-bone or 

 sphenethmoid (which represents several bones 

 joined together); this bone closes in the floor 

 >and sides of the forepart of the cranial cavity and 

 also its roof, being concealed in the latter place 

 by the anterior ends of the parieto-frontals. The 

 sphenethmoid has a single cavity behind, which 

 enters into the formation of the cephalic chamber, 

 and two cavities in front, one for each nasal 

 chamber, separated by a septum. 



c. Running out transversely from the girdle-bone 

 and the anterior end of the blade of the para- 

 sphenoid on each side, is the slender palatine. 



d. In front of the end of the blade of the para- 

 sphenoid and of the palatines are two broad 

 irregularly shaped bones, each bearing an oblique 

 row of teeth on its posterior part : these are the 

 vomers. 



e. The middle anterior boundary of the contour of 

 the skull, in this view, is formed by the denti- 

 gerous parts of the pre-maxillse ; and, behind 

 them, by the maxillae and the quadrato-jugal 

 bones (4. a. b). Running backwards from the 



