696 



rilK XKRVOUS SYSTEM 



the foraiiifii of Monro to the point where tlie cavity l)ifureates into its posterior 

 and deseendins: eornua. It corresponds ahno.-<t exactly in length to the portion of 

 the optic thalamus which lies free within the ventricular cavity. It is greatest in 

 its antero-posterior, and smallest in its vertical diameter. It is Hmited on the inner 

 side by the attachment of the fornix to the corpus callosum, and by the narrow 

 posterior part of the septum lucidum. On the outer side it is bounded by the fibre- 

 of the corpus callosum entering the substance of the hemisi^here. Its floor looks 

 upwards and slightly inwards, as can be well seen in coronal sections, and is formed 

 by a series of structures which trend forwards with an inclination inwards. Thes(- 

 structures are ]ilaced in the following order from without inwards: — the caudati- 

 nucleus of the corpus striatum, the ttenia semicircularis and lamina cornea, the 

 optic thalamus, the choroid plexus and the fornix (figs. 414 and 419). 



The anterior cornu is directed forwards, downwards, and outwards. It appear^ 

 crescentic in outline both in coronal and horizontal section. The concavity of the 

 crescent looks downwards and outwards, and is caused b}' the projection of the 



Fig. 416.- 



-COEOXAL SeCTIOX OF THE HEAD PASSING THROUGH THE POSTERIOR HoRXS OF 



THE Lateral Ventricles. 



(From a mounted specimeu iu the Anatomical Department of Trinity College, Dublin. 



Dura mater 



Br LB OF 



POSTERIOR 



CORNU 



HIPPOCAM- 

 PLS xMISOJ: 



FAsncrus 



LOSalTiDl- 



y.xLis jy- 



FERIOR 



Savri'ir 

 loiiyitudinal 

 sinus 



Falx cerebri 



Strnighl sinus 

 POSTERIOR 



coRyr OF 



LATERAL 

 VEyTRICLE 



CALCARiyE 

 FISSL'RE 



Lateral sinus CORPUS PEyiATUM Tentorium cerebeUi 



caudate nucleus into the cavity. The anterior cornu is bounded internally by the 

 septum lucidum, which forms a thin vertical partition between the anterior eornua 

 of opposite sides, al>ove and in front by the corpus callosum, and behind and 

 externally by the head of the caudate nucleus. 



The posterior cornu is horizontal in its whole course, and is directed at first 

 backwards and outwards, and afterwards backwards and inwards. It presents on 

 its inner wall a curved prominence, the hippocampus minor or calcar avis ; and 

 al)ove this a second prominence, the bulb of the cornu, whk-h is caused bv a part 

 of the force])s major projecting into the cavity. The hipiiocampus minor is caused 

 ])y a fold of the cerel)ral wall, and corresponds to the calcarine fissure on the 

 mesial surface of tlie hemisphere (fig. 41()). Its floor i)resents a slight elevation, 

 caused by the fasciculus longitudinalis inferior. 



Dissection.— Tiie operculum should next be pulled uiiwards, when the small portion of sub- 

 stance still attaching it to the brain will be broken through. A complete view of the island of 



