THE THALAMENCEPHALOX. 



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 cui-ves 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), [Lobus ventrmdl tertii, 

 Stieda; Thalaml ojjtici, Keissner; Thalamus opticus s. Lohus ventri- 

 culi tertii, Stannius ; Ganglien der Haemisphaeren, Cai-us). 



a. External form. From above (Fig. 98 Tho) the thalamence- 

 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 [Glandula pinealis). On removing the choroid plexus a small 

 apertm-e is seen in the roof of the thalamencephalon, connecting 

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

 The ventricle appears as a narrow slit in the median line, its 

 walls being formed by the optic thalami. By ^'g- io5- 



pressing aside the cerebral hemispheres the pos- 

 terior comnaissure [Covimissura 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 Ad) for some distance, and terminates in 

 a fine thread of connective-tissue. 



The inider surface of the thalamencephalon 

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

 optic chiasma {Clio) : the anterior portion 

 (Lf) is the lamina terminalis [Suhstantia cinerea 

 anterior)', the posterior {Tu.c) the tuher cine- 

 reum. The lamina terminalis is bounded on 

 either side by the cerebral hemispheres. The 

 tuber cinereum (Figs. 102, 103 Tit.c) is a small 

 median swelling immediately behind the optic 

 chiasma, and caused by the depression of the 

 floor of the third ventricle to form the iiifuu- 

 dibulinn [Diverticulum infundibidi, Reissner). 



Horizontal section tlirough 

 the brain to show the ven- 

 tiicles. 

 Aq Ventricles of optic lobes 



and the aqueduct of 



Sylvius. 

 Dv Third ventricle. 

 MF Foramen of Monroe. 

 Sv Lateral ventricle. 

 Vv Fourth ventricle. 



