1'HH THALAMENCBPHALOK. 



153 



the pigment line passes, first, directly outwards ; then suddenly turns 

 upwards and slightly outwards parallel with the wall of the deeper 

 part of the cavity ; it then curves outwards to pass below the cavity of 

 the optic lobe, where it divides, one portion passing outwards, the other 

 between the Sylvian aqueduct and the ventricle of the optic lobe. 



d. The Thalamencephalon (Huxley), (Lohus vent r icv.lt. tertii, 

 Stieda ; Thalami opt id, Reissner; Thalamu* optic us #. Loin* ventn- 

 culi tertii, Stannius ; Ganglien der Haeniisphaeren, Cams). 



a. External form. From above (Fig. 98 T/io) the thalamenee- 

 phalon is seen as a lozenge-shaped mass lying in front of the optic 

 lobes, and behind and between the diverging posterior ends of the 

 cerebral hemispheres ; it is covered by a thick vascular membrane, the 

 choroid plexus, through which passes the pedicle of the pineal 

 body ( Ghinilula pmeaK*). On removing the choroid plexus a small 

 aperture is seen in the roof of the thalamencephalon, connecting 

 the hollow pedicle of the pineal gland with the third ventricle. 



the median line, its 

 Fig. 105. 



in 



The ventricle appears as a narrow slit 

 walls being formed by the optic thalami. By 

 pressing aside the cerebral hemispheres the pos- 

 teriqr commissure (Com miss lira posterior] may 

 be seen lying quite in front and deep in the 

 cleft of the ventricle. Immediately behind the 

 pedicle of the pineal body is a slight but well- 

 marked depression (Fig 98 G), the origin of 

 which has not been investigated (Wiedersheim). 



The choroid plexus 'is continued forwards 

 between the cerebral hemispheres (Figs. 98, 

 103 A/ 1) for some distance, and terminates in 

 a fine thread of connective-tissue. 



The under surface of the thalameneephalon 

 (Fig. 102) is divided into two parts by the 

 optic chiasma (C/to) : the anterior portion 

 (Lf) is the lamina terminally (SitLsfantia cinerea 

 anterior}; the posterior (Tu.c} the tuler cine- 

 re u m. The lamina terminal** is bounded on 

 either side by the cerebral hemispheres. The 

 tuber clnereum (Figs, ion, 103 Ttt.r) is a small 

 median swelling immediately behind the optic 

 chiasma, .and caused by the depression of the /. Third ^ntricie. 

 flour of the third ventricle to form the in fun- MF Fl>ramen uf Monroe - 



, .. 9 of I^ite nil ventricle. 



<t I'j ii( tail (Dirertic>ifi>m infi'niUfjit.H, Reissner). > Fourth ventricle. 



Horizontal section through 

 the brain to show the ven- 

 tricles. 



AH Ventricles t>f optic lobes 

 and the aqueduct of 



