Fig' 45' Frontal Section through Posterior Part of Nasal Cavity. 

 Fig. 46. Frontal Section through Sphenoidal Sinuses and Nasal Cavity. 



A section from a skull was hardened, together witli its soft parts, in formalin, 



and decalcified before further division into frontal sections. The section shewn 



in Fig. 46 passed about \(,th inch behind Fig. 45. 



In Fig. 45, the posterior part of the Antrum of HiGHMORE has been 

 cut on both sides; the 3 turbinated bones are well shewn. The great variations 

 met with in the sinuses accessory to the nasal cavity, are well shewn bj' the fact, 

 that, on the left, the most Posterior Ethmoidal Cell has, been cut by the section, 

 whilst, on the right, the Ethmoidal Cells did not extend so far back. The posterior 

 part of the orbit has also been divided by this section. The numerous Vessels 

 and Nerves which lie close together in the Cavernous Sinus, diverge and divide 

 into groups; the origin of the Ocular Muscles near them, are shewn in cross- 

 section. The Optic Nerve which has left the skull-cavity, in company with the 

 Ophthalmic Artery through the Optic Foramen, lies, enclosed by Dura Mater, to 

 the inner side of these structures. 



In Fig. 46 the Sphenoidal Sinuses (their openings into the nose are 

 shewn in Fig. 4,5) are laid open. They are separated from each other by a 

 median septum and occupy the body of the Sphenoid Bone. They often extend 

 as far (cf. Fig. 47) as the Sella in which lies the Pituitary Body; in fact, they ma}' 

 reach the Spheno-Occipital Synchondrosis. They form the most posterior part of 

 the inner wall of the Orbit (cf. Fig. 42) and may in some cases extend into the 

 Greater Wings of the Sphenoid Bone (cf. Fig. 16 Lateral Recess of tlie Sphenoidal 

 Sinus). In chronic inflammation of the nose, these may become the seat of 

 suppuration, and have to be opened, because their natural narrow opening into 

 the nose affords insufficient drainage. 



In most cases, it will be possible to open them from the Nasal Cavity; 

 they are also accessible from in front, after having weU exposed the Ethmoidal 

 Cells from the Orbit (cf. Fig. 42). 



The Optic Nerve is cut as it enters the Optic Foramen. The Nerves from 

 the Cavernous Sinus lie close to each other in the Sphenoidal Fissure; below 

 them at some distance, is the 2nd division of the Vth Cranial Nerve. 



