THE SKULL AS A WHOLE 



177 



of the ethmoid bone, and serving for the transmission of the 

 divided olfactory nerves. Its median portion projects sHghtly into 

 the cranial fossa as a low ridge, the crista galli, which is interposed 

 between the tips of the olfactory bulbs. 



In the ventrolateral portion of the cranial cavity may be found 

 the internal openings of the foramina described above, namely, the 

 superior orbital fissure, the foramen lacerum, the jugular foramen, 

 and the hypoglossal canal. The superior orbital fissure is almost 

 ventral in position to the foramen opticum, and is connected back- 



co. 



Fig. 88. The skull in vertical section: B.O., basioccipital (basilar portion 

 of occipital) ; BS, basisphenoid (body of posterior sphenoid) ; ET, ethmo- 

 turbinal; F, frontal; I, interparietal; M, maxilla; MT, maxilloturbinal ; N, 

 nasal; NT, nasoturbinal; P, parietal; PL, palatine; PMX, premaxilla; PR, 

 presphenoid (body of anterior sphenoid); PT, petrous portion of petromastoid ; 

 SO, supraoccipital (squamous portion of occipital); T, tympanic; V, vomer, 

 a. p., piriform aperture of nose; c.f., internal aperture of facial canal; c.o., 

 occipital condyle; f.c.a., f.c.m., and f.c.p., anterior, middle, and posterior 

 cranial fossae; f.f., parafloccular fossa; f.h., hypophyseal fossa; f.in., incisive 

 foramen ;f.s., sphenopalatine foramen; 1., perpendicular plate of the ethmoid; 

 m.a.i., internal acoustic meatus; c, optic foramen; p. a., alveolar process of 

 maxilla; p.d., hard palate; p.o.e., external occipital protuberance; p.pt., 

 pterygoid process of posterior sphenoid; s.n., nasal septum; t.c, tentorium 

 cerebelli. 



ward with the foramen lacerum by a broad groove, the sulcus 

 sphenoidalis, which, in the natural condition, lodges the roots of 

 the fifth nerve. This groove continues to the medial surface of the 

 periotic bone, where it is bridged over by the tentorium cerebelli. 

 On the lateral wall of the posterior cranial fossa, and enclosed 

 by the compact, white, petrous portion of the periotic bone, is a 

 series of three apertures leading into its substance. One of these, 

 much larger than the remaining two, is the parafloccular fossa 

 (fossa parafloccularis) . It provides accommodation for the parafloc- 



