DISSECTION OF THE HEAD. 



Dissection 

 of third and 

 fourth 

 uerves ; 



of fifth 

 nerve. 



Third nerve 



passes to 

 orbit. 



Fourth 

 nerve 



in the wall 

 of sinus. 



Fifth nerve 

 has two 

 roots. 



Large root, 



Cavum 

 Meckelii, 

 and Gasse- 

 rian gang- 

 lion on it ; 



gives three 

 branches. 



Dissection. The third and fourth nerves, and the ophthalmic 

 trunk of the fifth nerve, lie in the outer wall of the cavernous 

 sinus ; and to see them, it will be necessary to trace them through 

 the dura mater towards the orbit. 



Afterwards the student should follow outwards the roots of the 

 fifth nerve into the middle fossa of the skull, as in fig. 189, taking 

 away the dura mater from them, and from the surface of the large 

 Gasserian ganglion which lies on the fore part of the petrous 

 portion of the temporal bone. From the front of the ganglion 

 arise two other large trunks beside the ophthalmic, viz., superior 

 and inferior maxillary, and these should also be traced to their 

 apertures of exit from the skull. If the dura mater is removed 

 entirely from the bone near the nerves a better view will be 

 obtained. Some of the nerves may have been injured by the 

 previous opening of the left cavernous sinus, and if that be so, the 

 dissectors should jointly examine the right side. 



The THIRD or OCULOMOTOR NERVE (fig. 189, 3 ) is destined for the 

 muscles of the orbit. It enters the wall of the cavernous sinus 

 near the anterior clinoid process, and is placed at first above the 

 other nerves ; but when it is about to enter the orbit through the 

 sphenoidal fissure, it sinks below the fourth and part of the fifth, 

 and divides into two branches. 



Near the orbit the nerve is joined by one or two delicate filaments 

 from the cavernous plexus of the sympathetic. 



The FOURTH or TROCHLEAR NERVE (fig. 189, 4 ) courses forwards to 

 one muscle in the orbit. It is the smallest of the cranial nerves, 

 and pierces the dura mater at the free edge of the tentorium, close 

 behind the posterior clinoid process. In the wall of the sinus it 

 lies below the third ; but as it is about to pass through the 

 sphenoidal fissure it rises higher than all the other nerves. 



While in the wall of the sinus the fourth nerve is joined by 

 twigs of the sympathetic. 



FIFTH or TRIFACIAL NERVE (fig. 189, 5 ). This nerve is distributed 

 to the face and head, and consists of two parts or roots a large or 

 sensory, and a small or motor. 



The large root of the nerve passes through an aperture in the 

 dura mater into the middle fossa of the base of the skull, where it 

 immediately enters the Gasserian ganglion. The hollow wherein the 

 ganglion is lodged is known as the Cavum Meckelii. 



The Gasserian ganglion, placed in a depression close to the apex 

 of the petrous part of the temporal bone, is flattened, and about 

 half an inch wide. The upper surface of the ganglion is closely 

 united to the dura mater, and presents a semilunar elevation, 

 the convexity of which looks forward. Some filaments from 

 the plexus of the sympathetic on the carotid artery join its inner 

 side. 



Branches. From the front of the ganglion proceed the three 

 following trunks : The ophthalmic nerve, the first and highest, is 

 destined for the orbit and forehead. Next in order is the superior 

 maxillary nerve, which leaves the skull by the foramen rotund urn, 



