GUIDE TO THE HEAD AND NECK 1567 



iully raised from the cerebellar fossse of the occipital bone, and the spinal 

 ■cord, vertebral arteries, and spinal accessory nerves are to be divided as low 

 down in the spinal canal as possible. 



The h^'poglossal, pnenmogastric, glosso-pharyngeal, anditory, facial, sixth 

 and third nerves are next to be di\-ided, as near as possible to where they 

 leave the cranial cavitv'. The infundibulam, in the median line, is to be cnt. 

 and anterior to it on either side the internal carotid artery is to be divided, 

 along with the optic nerve, which lies directly in front of it. The brain is 

 now to be entirely removed, care being taken to remove along with it the 

 olfactory lobes. 



Assuming the subject to be lying upon its back, the mode of procedure will 

 be the reverse of the foregoing. 



Before placing the brain in hardening fluid the base of the encephalon is 

 to be carefully studied. Its component parts are to be observed as follows : 

 the medulla oblongata, the pons Varolii, the cerebellum, and portions of the 

 cerebral hemispheres. The crura cerebri will be seen diverging from each 

 other above the pons ; anteriorly the optic tracts will be seen to converge 

 and form the optic comnrissirre ; and within the enclosed rhomboidal Jirea 

 there will be seen the locus perforatus posticus, the corpora albicantia, the 

 tuber cinereum, and a tag of the infundibulum. The stem of the fissure of 

 Syh-ins is to be noted, with the middle cerebral artery traversing it, and the 

 locus perforatus anticus at its inner end. In front of the fissure is the orbital 

 area of the frontal lobe of the cerebral hemisphere, and behind it the promi- 

 nent temporal lobe. The arachnoid and pia mater jire to be carefully examined. 

 Over the gj-ri they v^-ill be found to be in close contact, but in certain situations 

 intervals, called cistemae, exist between them. These are as follows : (i) cis- 

 "tema magna, between the cerebellum and the medulla oblongata ; (2) cistema 

 pontis, on the ventral aspect of the pons Varolii, in which the basilar artery 

 lies ; cind (3) cistema basaJis, over the interpeduncular region, in front of the 

 pons, and containing the circle of Willis. The superficial origins of the 

 o^nial nerves, including the olfactor\' lobe, are to be accurately observed, as 

 wen as the arrangement of the arteries. The arteries should be studied in 

 the following order : the two vertebrals, the basilar, the two posterior cere- 

 brals, the trunk of each internal carotid, the two anterior cerebrals, joined 

 by the anterior communicating, the middle cerebrals, and the two posterior 

 ■communicating arteries. In connection with the foregoing arteries the circle 

 of Willis is to receive careful attention. The anterior and posterior choroidal 

 arteries, as well as the lenticulo-striate arteries, are to be kept carefully in 

 "view. 



The arachnoid and pia mater are then to be removed as carefully as possible, 

 in order to expose the gyri and sulci to the influence of the hardening fluid. 

 In doing so a gentle stream of water may be advcintageous, but the cranial 

 nerves are not to be interfered with, though the arteries may now be taken 

 away. Thereafter the brain, base upwards, is to be carefully packed in a 

 crock containing hardening fluid, and laid aside for future dissection. 



Cranial Cavity. — The venous sinuses, cranial nerves, and arteries at the 

 base of the skull are next to be dissected. The superior longitudinzil sinus 

 along the upper border of the falx cerebri has been already studied. Along 

 the lower border of the falx cerebri the inferior longitudinal sinus, of small 

 size, is to be followed backwards into the straight sinus, which latter is situ- 

 ated along the line of junction of the falx cerebri and tentorium cerebeUi. 

 The occipital sinus is to be shown within the falx cerebelli along the course 

 ■of the internal occipital crest, as are also the inferior occipital or marginal 

 sinuses on either side of the vermiform fossa. The torcular Herophili is to 

 be laid open. It will usually be found upon the right side of the internal 

 ■occipital protuberance. The lateral sinus on either side is to receive very 

 ■careful attention, and in stud\-ing it the dissector should make himself familiar 

 with the line, upon the exterior of the head, which indicates its winding course. 

 This sinus should be laid open quite up to the postero-extemal compartment 

 of the jugular foramen. 



The cavernous sinus is then to be dissected with the greatest care, keeping 



