Skull and Hyoid 239 



This surface is flush with the jugum sphenoidale behind, where it is notched to 

 receive the " spine " of the sphenoid. 



The lower surface of the plate forms part of the roof of the nasal fossa, and is 

 therefore continuous in front with the small nasal areas on each side of the nasal spine 

 of the frontal. 



Vertical Plate. The crista galli comes above the horizontal plate as a thick process 

 to which the falx cerebri is attached, and from which strands of dura mater spread out 

 over the neighbouring bones. In front of it the foramen caecum of the frontal is placed, 

 so that the crista forms its back wall and broadens out into two ala to cover it. 



The rest of the vertical plate is in the septum, and is drawn down below into an 

 angle (Fig. 193), that fits in between the vomer, which articulates with its postero- 

 inferior border, and the cartilage of the septum, that is fastened to its antero-inferior 

 border. The upper and front part of the plate, just in front of the crista galli, comes in 

 contact with the nasal spine of the frontal between the small nasal areas on that bone, 

 and projects beyond this to support the two nasal bones. Behind, it comes up against 

 the crest and top of the rostrum of the sphenoid. It is covered by mucous membrane 

 and, deep to this, is grooved to carry olfactory fibres and their arachnoid coverings. 



The Lateral Mass is applied to the front of the sphenoidal turbinal : it rests below 

 on the inner and upper part of the maxilla, but its posterior part is separated from 

 this bone by the vertical plate of the palate. The os planum forms the greater part 

 of the inner wall of the orbital cavity : it does not, however, extend so far forward 

 as the rest of the mass, and the deficiency is filled by the lachrymal bone, which thus 

 articulates with the anterior margin of the os planum and partly covers in the exposed 

 " labyrinth." The os planum is in a plane with the side wall of the sphenoidal body 

 and turbinal, and the lachrymal connects it with the nasal process of the maxilla in 

 front. 



The labyrinth of the lateral mass consists of a number of air cells, with very thin 

 walls, that are arranged in groups anterior, middle, and posterior which do not 

 communicate directly. These cells are attached to the inner aspect of the os planum 

 and project into the cavity of the nose. From their inner surfaces thin curved sheets 

 of bone curve downwards and outwards and are known as the upper and middle turbinate 

 bones : they are, of course, only portions of the ethmoid. A scheme of the arrangement 

 is shown in Fig. 188. The middle turbinal comes down below the level of the lateral 

 plate and can be recognised at once. The middle meatus of the nose lies below the 

 middle turbinal, and the infundibulum runs up from the front part of this to the frontal 

 sinus, and the position of the infundibulum can be recognised on the bone (Fig. 188) 

 as a canal running upwards and forwards on the inner side of the mass that is exposed 

 in front of the os planum, and continues below with the groove below the middle 

 turbinal. 



It is evident that the lachrymal must cover in the infundibulum and form its outer 

 wall here if it is not separated from it by cells in this situation, which is the usual con- 

 dition : many incomplete cells may be seen round it which will be completed by the 

 lachrymal, frontal, and maxilla. 



An uncinate process passes downwards and backwards from the front and lower 

 part of the mass, outside the middle turbinal (Fig. 188), to articulate with the inferior 

 turbinate bone and partly fill in the opening of the maxillary antrum, but this is not 

 often seen complete on the disarticulated bone. 



If the lateral mass is removed and looked at from the inner side the upper and 

 lower turbinals are seen suspended from the inner wall of the ethmoidal cells : the 



