Sorensen, Study of Epiphysis and Roof of Diencephalon. 37 



stalk. This last, perhaps 3 mm. in transverse section and 2 

 mm. in longitudinal section, is nearly reniform, since it is elon- 

 gated dorso-ventrally, and shows a small invagination behind. 

 The whitish-grey surface appears rough as if granulated. Sand 

 is not present and was not to be expected in an animal so young. 

 The stalk, over 4 mm. long, joined to the anterior part of the 

 nodule is a structure composed of nervous tissue, which is also 

 represented in a dorso-ventral section. At first small (hardly 

 1 y 2 mm. wide) so that it is covered behind by the nodule, later 

 the stalk broadens during its course forward and finally divides 

 into two parts, namely, the two pedunculi conarii. These, as 

 in man, pass over laterally on each side into the trigonum hab- 

 enulae, while the unpaired stalk unites ventrally with the post- 

 commissure. The inner attenuated edges of the peduncles ter- 

 minate in the taeniae medullares of the thalami optici. The 

 pineal recess stretches far caudad nearly to the nodule, i. e., the 

 stalk is entirely hollow even to a small section of its hindermost 

 part. This can be easily verified by the introduction of a 

 bristle. 



A second pineal of a young chimpanzee studied was not in 

 a desirable condition as the caudal part was torn off. In it how- 

 ever this much can be established with certainty, that a similar- 

 ly developed, hollowed, unpaired stalk of the same length was 

 present. By means of Pal's method, the microscopic investiga- 

 tions brought out numerous well-marked longitudinal nerve 

 fibres which, moreover, were not spread throughout the entire 

 thickness of the wall of the stalk, but formed an outer continu- 

 ous layer. From a comparison of the relations as found here 

 with those found in man we obtain some noteworthy differences. 

 The unpaired stalk which in the case of the chimpanzee pineal 

 forms the principal stalk, is entirely wanting in the human pin- 

 eal and in connection with it the pineal recess is more noticeable 

 in every case. On the other hand the peculiar pineal body in 

 man attains an essentially stronger development than in the 

 chimpanzee, where the latter is represented only by a small 

 nodule. It is moreover possible that the pineal body in adult 

 chimpanzee attains a relatively greater development than in the 



