2i8 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 the 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-maxillae ; and, behind 

 them, by the maxillae and the quadrato-jugal 

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



