Turner, Mo7-p]iologv of tlic Avian Bra'ni. 4-^ 



in the prosencephalon. When there is only one lobe, it is 

 the result of the fusion of the primitive lobes. When two 

 lobes are present, each usually contains a ventricle; but when 

 there is only one lobe, it is usually solid. 



The above types merge into each other. As we ascend 

 the scale, the olfactory lobes move caudad aud become 

 smaller. In the higher groups, the lobes are fused and 

 almost completely imbedded in the prosencephalon. 



EXl'LANATION OF TABLE I (SEE P. 78). 



" Length " is a contraction for " Ratio of the length of the rhinenceph- 

 alon to the length of the brain." 



" Breadth" is a contraction for " Ratio of the breadth of the riiinen- 

 cephalon to the length of the brain." 



All ratios are expressed in hundredths of the length of the brain. 



" Partly imbedded " is a contraction for " Partly imbedded in the 

 prosencephalon." 



A ~(- affirms what is at the head of the column. 



A — denies what is at the head of the column. 



PROSENCEPHALON. 



Size. — In carinate birds, the prosencephalon is relatively 

 very large. In the birds examined, the dimensions vary in 

 different groups; thus, the ratio of the length of the prosen- 

 cephalon to the length of the brain varies from about 55 per 

 cent., in the Ardeidce., to about 92 per cent., in the Corvidce; 

 the ratio of the breadth of the prosencephalon to the length 

 of the brain varies from about So per cent., in the Ardeidic, 

 to about 135 per cent., in the Corvidce ; the ratio of the depth 

 of the prosencephalon to the length of the brain varies from 

 about 45 per cent., in the ArdcidiC, to about 68 per cent., in 

 the Corvidiv(^) (see Table II). 



In all types, the depth of the prosencephalon is less than 

 its length. In the Anatidir^ the length and breadth are about 



I After having carefully weighed the lirains of various European birds, A. Bumm 

 compiled the following table : 



Ratio of the Weight of the prosencephalon to the -weight of the remainder of the brain. 

 — In the oscinine birds, 2.79 : 1 ; in the fringilline birds, 2.77 : i ; in the parrots, 2.08 : i • 

 in the swimming birds, 1.94 : i ; in the wading birds (Sumpfvogel), 1.75 : i ; in the birds 

 of prey, i.6t : i ; in the fowls, 1.12 : i ; in the doves, 0.95 : i. Op. cit., p. 433. 



