68 PRACTICAL ANATOMY. 



The facial portion of the base forms the roof of the 

 mouth ; it is limited anteriorly by the posterior face of 

 the incisor and canine teeth, laterally by the inner face 

 of the bicuspids and molars. It is trilateral in outline, 

 a foramen being found at each angle, in front the ante- 

 rior palatine, and at each of the posterior angles the 

 posterior palatine foramen. Running backward, from 

 the anterior palatine foramen to the posterior nasal spine, 

 is the palatine crest, formed by the articulations of the 

 inner borders of the horizontal portions of the superior 

 maxillary and palate bones. The upper surface of the 

 base forms the floor of the cranial cavity and supports 

 the brain. It is divided into three fossae, anterior, 

 middle, and posterior. The anterior is the smallest, and 

 is situated on the highest plane; the posterior is the 

 largest, and occupies the lowest portion of the cranial 

 cavity; the middle fossa is on a lower plane than the 

 anterior. The anterior fossa is bounded in front and at 

 the sides by the frontal bone, and is limited behind by 

 the posterior border of the lesser wing of the sphenoid 

 and orbital plate of the frontal. It supports the ante- 

 rior lobes of the brain. It is convex from side to side 

 and smooth, although impressed by the convolutions of 

 the brain. In the middle line is the crista galli of the 

 ethmoid, which affords attachment to the falx cerebri. 

 On each side are the olfactory foramina in the cribriform 

 plate of the ethmoid; these foramina transmit the fila- 

 ments of the olfactory nerves to the nose. In front of 

 the crista galli is a pit called the foramen cascum, which 

 sometimes exists as a canal, and transmits a small vein ; 

 it is the point of origin of the great longitudinal sinus. 

 The middle fossa is strongly concave and irregular; it 

 supports the temporo-sphenoidal and middle lobes of the 

 brain. It is limited in front by the posterior edge of the 



