Turner, Morphology of tiic Avian lirai, 



47 



At first sight these two fissures appear to be distinct, but 

 I have considered them identical: 



I. Because Bumm has done so.(') 



3. Because both are never found in the same species. 



3. Because I find all the intermediate stages. 



In the Anatidcc (Plate V, Fig. 10, DF) this fissure lies 

 entirely vxpon the dorsal surface of the brain and is very long. 



In the Picidcc (Plate V, Fig. 10, DF) it lies upon the dor- 

 sal surface of the prosencephalon, but it is near the cephalic 

 extremity of the same. It is also very short. In the Cjich- 

 lidce^ ArdeidiC^ Mclcagrididcp and Strigidcc this fissure arises 

 from the ventral surface of the brain, betw^een the origin of 

 the rhinencephalon and the cephalad extremity of the prosen- 

 cephalon and terminates upon the dorsal surface of the cere- 

 bral hemisphere (Plate V, Figs. 1,4, 6, 8; DF). 



In the Ictcridiv (Plate V, Fig. 7) it arises from the ven- 

 tral surface of the prosencephalon caudad to the rhinen- 

 cephalon and terminates upon the dorsal surface of the 

 cerebral hemisphere. 



Dorsal tuber. — The dorsal fissure either partly or entirely 

 surrounds a slight swelling. This swelling I have called the 

 " dorsal tuber." Since the dorsal fissure surrounds the dorsal 

 tuber, whenever a portion of that fissure is on the ventral 

 surface of the brain, a portion of the dorsal tuber is also car- 

 ried ventrad. 



On the ventral surface are several tubers. These may be 

 studied to the best advantage in the owl brain [Bubo virgin - 

 ian7ts) , where they are enormously developed (Plate V, Fig. i ). 

 J'entro-frontal tuber (Plate V, Figs, i, 13). — This is a 

 small swelling which is situated upon the ventral surface of 

 the prosencephalon at the meson and near the cephalad 

 extremity of the hemispheres. When this tubei is present, 

 the rhinencephalon is situated immediately ventrad to it. 



I Op. cit.; T:if. 24; Figs, i, 5; WF. 



