326 



HEAD AND NECK 



very important to preserve these apertures intact, so that the proximal 

 ends of the nerves may be held in position during the dissection. The 

 incision through the dura mater may now be carried postero-laterally along 

 the upper border of the petrous bone in the line of the superior petrosal 

 sinus, and antero-laterally along the posterior margin of the lesser wing of 

 the sphenoid. After the incisions are made raise the dura mater with great 

 care, for it is intimately connected with the nerves which lie subjacent to 

 it. Thus, where it forms the lateral wall of the cavernous sinus, it 

 is closely applied to the oculo- motor and trochlear nerves, and firmly 

 attached to the ophthalmic division of the trigeminal nerve, whilst over 

 the petrous bone it is united to the surface of the semilunar ganglion. 

 The edge of the knife, therefore, must be kept close to the membrane, and 

 a small portion of the membrane may be left upon the nerves. This can 

 be removed afterwards as the nerves are defined. 



Sinus Cavernosus. The cavernous sinus has been opened 



NT. CAROTID I N F U N D I B U LU M 



OCULO-MOTOR 

 TROC HLEAR 



FIG. 129. Section through the Cavernous Sinus. (After 

 Merkel, somewhat modified. ) 



by the above dissection. It is a short, wide venous channel, 

 which extends along the side of the body of the sphenoid bone, 

 from the lower and medial end of the superior orbital fissure 

 (O.T. sphenoidal fissure) to the apex of the petrous portion 

 of the temporal bone. Anteriorly, blood is conducted into it 

 by the ophthalmic veins and the spheno-parietal sinus ; whilst 

 posteriorly the blood is drained away by the superior and 

 inferior petrosal sinuses. But it has still other connections. 

 Thus, it receives blood from the lower part of the lateral 

 surface of the brain by the superficial middle cerebral vein 

 and some small inferior cerebral veins. It is united with 

 the corresponding sinus of the opposite side by means of the 

 anterior and posterior intercavernous sinuses (p. 2 1 7). Lastly, 

 one or more emissary veins leave its lower aspect ; one passes 

 out of the cranium by the foramen ovale, or it may be 



