288 LILY C. SHUDDEMAGEN. 



The anterior commissure (PL XXIV., Fig. 3, Coin. A) is of fairly 

 large size. It is a rather cylindrical bundle of fibers and connects 

 the pyriform lobes. Because of the relatively large size of the 

 pyriform lobes, the anterior commissure attains its increase of 

 size. In the armadillos, all the parts of the brain connected with 

 the sense of smell, reach relatively large dimensions. 



(ft) Thalamencepkalon. - - The thalamencephalon is the second 

 embryological division of the brain, and consists of that part 

 which bears the optic thalami, the infundibulum, pituitary body, 

 and pineal body. 



The optic thalami (PL XXV., Fig. 7, Opt. Th) and the corpora 

 quadrigemina (PI. XXV., Fig. /, Cor. Q.) form a large area of 

 quadrilateral shape. The optic thalami are separated from each 

 other, in the median line, by the third ventricle. They are con- 

 nected across this ventricle by means of the comrnissura molli. 

 This extends across the slit-like third ventricle as a large cylin- 

 drical mass of fibers (PI. XXIV., Fig. 3, Com. Mol.). Thus the 

 third ventricle becomes reduced to a narrow circular channel sur- 

 rounding the commissura molli. 



The floor of the third ventricle is drawn downward into a 

 funnel-shaped pouch, the infundibnhnn (PI. XXIV., Fig. 3, Inf.). 



The hypophysis (PI. XXIV., Fig. 3, Hyp.) is attached to the 

 ventral part of the infundibulum. 



The pineal body (PL XXV., Fig. 7, Cor. Pin.) lies in a shallow 

 groove of the anterior corpora quadrigemina, just posterior to 

 the third ventricle. 



The third ventricle (PL XXV., Fig. 7, Veil. Ill) opens into 

 the two first ventricles (PL XXV., Fig. 7, Ven. I) by means of 

 the foramen of Monroe (PL XXV., Fig. 7, For. M.). Out of 

 the posterior part of the third ventricle, the aqueduct of Sylvius 

 (PL XXIV., Fig. 3, Aq. Syl) opens and passes into the fourth 

 ventricle. 



The //, or optic nerve (PL XXIV., Fig. I, //) comes off from 

 the ventral surface of the brain, just a little anterior to the infundi- 

 bulum. It is of very small size, because of the great diminution 

 of the visual acuteness and consequent reduction of the size of 

 the eye. 



The IV, or pathetic nerve (PL XXIV., Fig. i, IV) arises from 



