THE LIZARD. 181 



248. The third ventricle (r. 3), a narrow vertical slit 

 between the optic thalami, continuing forwards the aqueduct 

 of Sylvius : it communicates in front by the foramen of 

 Monro (//), already seen ( 245), with the lateral ventricle. 



249. The anterior commissure (a.c\ a small, trans- 

 verse band of white nerve fibres, passing transversely 

 between the two optic thalami, below and somewhat in front 

 of the foramen of Monro. 



250. The posterior commissure (p.c), a similar trans- 

 verse band connecting the optic thalami at their junction 

 with the mid-brain. 



XXIX. Cut away the remainder of the left side of the 

 brain so as to get a longitudinal vertical section of 

 the whole organ (Fig. 45, D). Note : 



251. The continuity between the fourth ventricle, aque- 

 duct of Sylvius, and third ventricle, and the precise position 

 of the apertures leading into the lateral and optic ventricles. 



252. The downward continuation of the third ventricle 

 into the infundibulum. 



253. The general relations of the parts seen in the 

 previous dissection. 



