^ruRNKK. Morpliolo^x of the Avian Hraiii. (^\ 



It will be noticed that the Turdida^ have been placed 

 lower in the scale than either the Tanagrida^, the Fringillida', 

 or the Icterida?. R. W. Shufeldt places the Tiirdidje in about 

 the same position. In defending his position, Mr. Shufeldt 

 remarks, that the reduction of ten primaries to nine is an 

 index of great specialization; he then adds: "The Tanagers 

 show this feature; and it is a good one to hold them in 

 the place which I have assigned them; moreover, it gives 

 them precedence over the more lowly organized Turdida;, 

 which in realty should long ago have been recognized."(') 



RECAPITULATION. 



1. The avian prosencephalon is large, but is not convoluted. 



2. The avian epencephalon is well developed and trans- 

 versely convoluted. 



3. From the introduction of the class Aves until now, 

 there has been a gradual retrograde evolution of the avian 

 rhinencephalon. In the lowest type of birds, the rhinenceph- 

 phalon is double and projects beyond the cephalic extremity 

 of the prosencephalon; in the highest type the rhinenceph- 

 alon is single and does not project beyond the cephalic 

 extremity of the prosencephalon. 



4. In the lower types of avian brains the optic lobes are 

 only partially covered by the prosencephalon; in the higher 

 types the optic lobes are entirely covered. 



5. During both the evolution of the class Aves and the 

 diflerentiation of the families within it, the dorsal and lateral 

 portions of the avian prosencephalon have grown caudad 

 much more rapidly than the ventral and mesal portions. 

 This has caused the caudal portion of each cerebral hemis- 



young differ in their plumage from the parents, and while we do not yet know the exact 

 affinities of the Hirundinidae, all the speculations in that quarter have been in the direc- 

 tion of associating them with groups of recognized low type of organization." Op.cit.,p.iio. 

 Although the brain of the Hirundinidae may be relatively small, yet it is as highly 

 developed as the brain of either the Tanagridae or Icteridae. C. H. T. 



I Op. cit., p. 109. 



