28 



DISSECTION OF THE HEAD. 



The lateral sinus (fig. 3, e) is the channel by which most of the blood 

 passes from the skull. There is one on each side, right and left, which 

 extends from the occipital protuberance to the foramen jugulare, where it 

 ends in the internal jugular vein. In this extent the sinus occupies the 

 winding groove in the interior of the skull between the two points of bone 

 before mentioned : and the right is frequently larger than the left. 



Fig. 3. 



a. Torcular Herophili. 



6. Superior longitudinal sinus. 



c. Inferior longitudinal. 



d. Straight sinus. 



e. Lateral sinus. 

 g. Occipital sinns. 



/. Superior, and h, inferior petrosal sinus. 



SOUK OF THE SlSUSES OP THE SKULL. 



Besides small veins from the brain, it is joined by the superior petrosal 

 sinus (f), opposite the upper edge of the petrous portion of the temporal 

 bone ; and by the inferior petrosal (h) at the foramen jugulare. Often- 

 times it communicates with the occipital vein through the mastoid fora- 

 men, and sometimes with veins of the diploe of the skull. 



The foramen jugulare is divided into three compartments by bands of 

 the dura mater. Through the posterior interval the lateral sinus passes ; 

 through the anterior the inferior petrosal sinus; and through the central 

 one the pieces of the eighth nerve. 



Dissection. To examine the cavernous sinus on the left side, cut 

 through the dura mater by the side of the body of the sphenoid bone from 

 the anterior to the posterior clinoid process, and internal to the position of 

 the third nerve : behind the clinoid process, let the knife be directed in- 

 wards for about half the width of the basilar part of the occipital bone. 

 By placing the handle of the scalpel in the opening thus made, the extent 

 of the space will be defined. A probe or a blow-pipe will be required, in 

 order that it may be passed into the different sinuses joining the cavernous 

 centre. 



B. The CAVERNOUS SINUS, which has been so named from the reticu- 

 late structure in its interior, is situate on the side of the body of the 

 sphenoid bone. This space, resulting from the separation of the two 

 layers of the dura mater, is of an irregular shape, and extends from the 

 sphenoidal fissure to the tip of the petrous portion of the temporal bone. 



The piece of dura mater bounding the sinus externally is of some thick- 

 ness, and contains in its substance the third and fourth nerves, witli the 

 ophthalmic trunk of the fifth nerve ; these lie in their numerical order 

 from above down. 



The cavity of the sinus is larger behind than before, and in it are 

 shreds of fibrous tissue with small vessels. Through the space winds the 



