INTERNAL CAROTID ARTERY. 33 



One of these (cavernous) is near the root of the anterior clinoid pro- 

 cess ; and to bring it into view it will be necessary to cut off that piece of 

 bone, and to dissect out with care the third, fourth, fifth, and sixth nerves, 

 looking for filaments between them and the plexus. Another plexus 

 (carotid), joining the fifth and sixth nerves, surrounds the artery as this 

 enters the sinus. 



The INTERNAL CAROTID ARTERY appears in the base of the skull at 

 the apex of the petrous part of the temporal bone. In its ascent to the 

 brain the vessel lies in the space of the cavernous sinus, along the side 

 of the body of the sphenoid bone, and makes two remarkable bends, so as 

 to look like the letter S reclined. At first, the artery ascends to the 

 posterior clinoid process ; it is then directed forwards to the root of the 

 anterior process of the same name ; and lastly it turns upwards internal 

 to this last point of bone, perforates the dura mater bounding the sinus, 

 and divides into cerebral arteries at the base of the brain. In this 

 course the artery is enveloped by nerves derived from the sympathetic in 

 the neck. 



The branches of the artery here are few. In the sinus there are some 

 small arteries (arteriae receptaculi) for the supply of the dura mater and 

 the bone, the nerves, and the pituitary body ; and at the anterior clinoid 

 process the ophthalmic branch arises. 



The terminal branches of the carotid will be seen in the dissection of 

 the base of the brain. 



SYMPATHETIC NERVE. Around the carotid artery is a prolongation of 

 the sympathetic nerve of the neck, which forms the following plexuses : 



The carotid plexus is situate on the outer side of the vessel, at its en- 

 trance into the cavernous sinus, and communicates with the sixth nerve 

 and the Gasserian ganglion. 



The small cavernous plexus is placed below the bend of the artery which 

 is close to the anterior clinoid process, and is connected with that offset 

 of the upper cervical ganglion which courses along the inner side of the 

 carotid artery. Filaments from the plexus unite with the third, fourth, 

 and ophthalmic nerves. One filament is also furnished to the lenticular 

 ganglion in the orbit, either separately from, or in conjunction with, the 

 nasal nerve. 



After forming those plexuses, the nerves surround the trunk of the 

 carotid, and are lost chiefly in the cerebral membrane named pia mater ; 

 but some ascend on the cerebral and ophthalmic branches of that vessel, 

 and one offset is said to enter the eyeball with the central artery of the 

 retina. 



Petrosal nerves (fig. 34). Beneath the Gasserian ganglion is the large 

 superficial petrosal nerve (fig. 34, z ) entering the hiatus Fallopii to join 

 the facial nerve. Externally to this is occasionally seen another small 

 petrosal nerve (fig. 34, 4 ) (external superficial), which springs from the 

 sympathetic on the middle meningeal artery, and enters the bone to join 

 the facial nerve. A third, the small petrosal nerve (fig. 34, 3 ), is con- 

 tained in the substance of the temporal bone. The source, and the desti- 

 nation of those three small nerves will be afterwards learnt. It will suffice 

 now for the student to note the two first, and to see that they are kept 

 moist and fit for examination at a future time. 



Directions. Now the base of the gkull has been completed, a preserva- 

 tive fluid or salt should be applied, and the flaps of the teguments should 

 be stitched together over all. 

 3 



