NASAL CAVITIES AND AIR SINUSES. Go 



hind by the dorsum sellge. The lateral part on each side, formed by 

 the great wing of the sphenoid, the squamous part, and the anterioi* 

 surface of the petrous part of the temporal, lodges the temporal lobe of 

 the brain. The foramina of the middle fossa are the foramen opticum, 

 the sphenoidal fissure, foramen rotundum, foramen ovale, foramen 

 spinosum, foramen lacerum anterius, and hiatus Fallopii. 



The posterior fossa, deeper and larger tUan the others, extends back 

 to the occipital protuberance, and lodges the cerebellum and medulla 

 oblongata. The occipital bone and the petrous and mastoid portions 

 of the temporal bone take part in its formation. In the posterior 

 surface of the pars petrosa, which limits this fossa anteriorly on each 

 side, is the internal auditory meatus ; lower down is the foramen 

 lacerum posterius ; between that and the foramen magnum is the 

 anterior condylar foramen. 



Grooves for Bloodvessels. — The groove of the middle meningeal 

 artery commences at the foramen spinosum of the sphenoid bone, and 

 ramifies principally on the squamous portion of the temporal bone and 

 on the parietal. The groove of the internal carotid artery lies on the 

 side of the body of the sphenoid bone, and terminates inside the anterior 

 clinoid process. The groove of the superior longitudinal sinus, com- 

 mencing at the foramen coecum, passes backwards in the middle line of 

 the roof of the skull, and terminates at the internal occipital protuber- 

 ance. From that point the grooves of the lateral sinuses pass outwards 

 on the occipital bone, cross the posterior inferior angles of the parietal 

 bones, descend on the mastoid portions of the temporal bones, run 

 inwards again on the occipital, and turn forwards to terminate at the 

 jugular foramen. The groove of the inferior petrosal sinus lies between 

 the petrous portion of the temporal bone and the basilar process ; that 

 of the superior petrosal sinus extends along the superior angular edge 

 of the petrous portion. 



THE NASAL CAVITIES AND COMMUNICATING AIR SINUSES. 



The nasal cavities, or fossaj, are placed one at each side of a median 

 vertical septmn. They open in front and behind by the anterior and 

 posterior nares already described, and communicate by foramina with 

 the sinuses of the frontal, ethmoid, sphenoid, and superior maxillary 

 bones. Their vertical extent, as well as that from before backwards, 

 is considerable, but their transverse width is very limited, especially 

 in the upper part. 



The internal ivall, or septum narnim, is formed principally by the 

 central plate of the ethmoid bone, the vomer, the frontal spine, the 

 rostrum of the sphenoid bone, and the crests of the maxillary and palate 

 bones. It presents a great angular deficiency in front, which in the 

 recent state is filled up by the septal cartilage. In very many cases it 

 deviates from the middle line, and more frequently to the left than to 

 the right side. 



The roof is, horizontal in its middle part, but sloped downwards be- 

 fore and behind. The middle part is formed by the cribriform plate of 

 the ethmoid bone, the fore part by the frontal and nasal bones, and the 

 back part by the sphenoidal spongy bone. 



The /oor, formed of the palate plates of the maxillary and palate 

 bones, is smooth, and concave from side to side. Towards its anterior 

 extremity is the superior orifice of the incisor canal. 



