Turner, Morphology of the Avian Brain. 69 



ally I have noticed cells with two well developed nuclei. 

 Sometimes the nucleus is sub-spherical (Plate VIII, Fig. i). 



Masked convolution. — In the brain of Swainson's thrush 

 [Hylocichla swainsoni) I have noticed a masked convolution. 

 Near the mesal extremity of the parieto-occipital lobe and 

 about half way between the dorsal and ventral surface of the 

 prosencephalon a narrow projection of the parieto-occipital 

 lobe extends entad. Within the axial portion of the brain 

 this projection widens and form an ellipsoidal body. This 

 small ellipsoidal body is histologically distinct from the region 

 in which it is found, but it is histologically identical with the 

 parieto-occipital lobe. The region around it is composed of 

 fusiform nerve cells (Plate VIII, Fig. 13), while it is com- 

 posed of pyramidal cells (Plate VIII, Fig. 6). 



Parieto-frontal Lobe (Plate VI, Fig. 1, P. F. L.).— This 

 lobe forms the middle portion of the lateral division of the 

 mantle and extends from the parieto-occipital lobe to the 

 fronto-median. It consists of two layers: 



1. A narrow outer layer of free cortex. 



2. A wider inner layer containing many Deiter's corpuscles 

 and a few scattered nerve cells. This is the parieto-frontal 

 nidulus. Near the cephalic portion of this lobe the cells are 

 more abundant than elsewhere. These cells are pyramidal 

 in outline and have either convex or straight sides. The 

 apex is extended into a long process, while the base is sup- 

 plied with several shorter processes. These cells stain 

 densely and have an elongated dense nucleus and denser 

 nucleolus. 



Frontal Lobe. — This lobe forms the cephalad portion of 

 the lateral division of the mantle. As has been mentioned 

 above, a portion of it extends caudad between the cephalad 

 portion of the fronto-median lobe and the meson. Dorsad it 

 fuses with the parieto-frontal lobe and spreads over the 

 greater portion of the dorsal surface of the hemisphere. 

 Ventrad it is bounded by the fronto-median lobe (Plate VI, 



