THE SKULL. 59 



squamous portions of the temporals (4), frontals (s), the 

 sphenoid (5), and presphenoid (e). A slight rounded ridge 

 on its lateral wall at about the position of the suture between 

 the frontals and parietals separates a smaller cranial portion 

 sometimes called the anterior fossa, from a larger caudal por- 

 tion sometimes known as the middle fossa of the cranial cavity. 

 The walls of the cerebral cavity are marked with numerous 

 ridges and shallow furrows for the cerebral convolutions. 



The floor of the cerebral cavity is bounded caudad by the 

 prominent dorsum sellae (Fig. 42,/; Fig. 43, g), just craniad 

 of which is the rounded depression known as the sella turcica 

 (¥\g. 42, g\ Fig. 43, h), for lodgment of the hypophysis. A 

 number of foramina pierce the floor of the cavity in this region. 

 Just ventrad of the cranial tip of the petrous portion of the 

 temporal is the small foramen lacerum (medius). Craniad 

 and laterad of this is a row of four foramina : the caudal one is 

 the foramen ovale (Fig. 42, z); then come in order the foramen 

 rotundum (y'), the orbital fissure {k), and the optic foramen 

 (Fig. 42, /; Fig. 43, k). The two optic foramina are connected 

 by the shallow transverse chiasmatic groove (Fig. 42, ;;/), for 

 the optic chiasma. Another small foramen continues caudad 

 from a groove on the floor of the orbital fissure ; this opens on 

 the ventral surface of the sphenoid, between the wing and the 

 body of the bone. The groove and foramen constitute the 

 pterygoid canal, which transmits a nerve, — the nerve of the 

 pterygoid canal, or Vidian nerve. 



The cranial cavity narrows at its cranial end to form the 

 small olfactory fossa (Fig. 43, ///) which lodges the olfactory 

 bulbs. This is bounded by the frontals and the lamina cribrosa 

 (Fig. 42, o) of the ethmoid; caudad it opens directly into the 

 cerebral fossa. Numerous openings through the lamina 

 cribrosa for the olfactory fibres connect the olfactory fossa with 

 the nasal cavity. The roof of the fossa is marked by a promi- 

 nent median crest from the united edges of the frontals. 



The nasal cavity is almost completely filled by the ethmoid 

 and vomer and the conchae nasales. Its roof is formed by the 

 nasal bones and portions of the frontals; its sides by the 

 frontals, lachrymals, maxillaries, premaxillaries, and palatine 



