THE HEAD AND NECK. 139 



Find the following fissures and their contents : 



1. Tlie great longitudinal fissure contains : (i) The falx cerebri with its 

 superior and inferior longitudinal sinuses ; (2) the corpus callosum, on which 

 you may see the anastomosis between the anterior and posterior cerebral 

 arteries. 



2. The great transverse fissure, between the occipital cerebral lobes and the 

 cerebellum. It contains the tentorium cerebelli. 



3. The fissure of Sylvius, bounded below by the temporo-sphenoidal lobe; 

 above by the frontal and parietal lobes. It contains : (i) The island of Reil, or 

 central lobe of the cerebrum ; (2) the middle cerebral artery and vein and their 

 numerous branches. 



4. The fissure of Rolando is between the ascending convolutions of the frontal 

 and parietal lobes. Its surgical importance is due to the fact of the location of 

 the cortical motor areas about this fissure. 



5. The occipito-parietal fissure is very imperfect. As its name implies, it is 

 between the parietal and occipital lobes. 



Dissection of the brain does not belong to dissecting-room anatomy, hence 

 the reader is referred to Morris for this very interesting and instructive part of 

 anatomy. 



THE ORBIT AND ITS CONTENTS. 



For dissecting-room purposes, the following points seem of practical or 

 rather demonstrable importance : 



i. Geometry of the Orbit. Roof, floor, outer wall, inner wall, base, apex, 

 angles, and cavity. 



The roofis of importance, since it separates the cavity of the orbit from the 

 frontal lobes of the brain. A missile may reach the brain in this way, since this 

 roof is often very thin. 



The floor is of importance (i) because it forms a partition between the orbit 

 and the antrum of Highmore, or maxillary sinus ; (2) because it is traversed by 

 the infraorbital canal, in which are the infraorbital nerve and vessels. 



The inner wall is in close relation with the nasal fossae, and the ethmoid cells, 

 the os planum of the ethmoid, and the lachrymal bones form a large part of the 

 partition between these cavities. 



The outer wall is formed by the orbital plates of the sphenoid and malar 

 bones, but is of no special importance. 



The apex of the orbit transmits the optic nerve and the ophthalmic branch 

 of the internal carotid artery. The apex is occupied by the optic foramen, be- 

 tween the two pedicles of the lesser ala of the sphenoid bone. 



The base of the orbit is of great importance on account (i) of its architectural 

 construction, combining beauty, strength, and protection ; (2) of the large num- 

 ber of anatomical structures in this region. 



Note about the base of the orbit : 



1. The laclirymal gland (Fig. 104), under the external angular process of 

 the frontal bone, in a fossa called the lachrymal fossa. This is called the orbital 

 part of the gland or the superior lachrymal gland ; the part of the gland that 

 protrudes below this is called the palpebral portion or the inferior lachrymal 

 gland. 



2. The S2ipraorbital foramen (it may be double) transmits the supraorbital 

 nerve and vessels. (Figs. 98, 103.) The vessels are branches of the ophthalmic. 



