142 HUNTINGTON. 



metrically into the secondary branches A' and A" . The cor- 

 responding arteries are situated ventrad, derived from the pul- 

 monary artery close to its division into right and left main 

 trunks. 



In conformity with the complete bilateral symmetry of the 

 tree a cardiac bronchus is not present. 



SUMMARY. 



If we briefly sum up the main facts just deduced from the 

 examination of these specimens we find that a complete con- 

 secutive series can be established, leading from the symmetrical 

 " bilateral hyparterial type " without cardiac bronchus {Hystrix), 

 through gradual modifications, to the complete symmetrical 

 "bilateral eparterial type" without cardiac bronchus {Phocci). 



This series, to obtain a comprehensive view of the main fea- 

 tures, may be schematically represented in PI. XXVII. 



Based on this comparison we may incorporate our conclu- 

 sions in the following propositions : 



1. The right and left lung agree, morphologically, in the 

 type of their bronchial distribution. 



2. The asymmetry — when observed — is apparent, not real, 

 depending usually upon complete separation of the right 

 cephalic trunk A into its two components A' and A'\ and 

 migration of A' cephalad, changing its original relation to 

 bronchial stem and pulmonary artery ; more rarely the asym- 

 metry depends upon the complete migration cephalad of the 

 entire trunk A^ carrying the secondary branches A' and A'^ 

 {]\'Iyrinccopliag a) . 



3. Aeby's hypothesis of the morphological equivalence of 

 the middle right and upper left lobe of the human lung is, 

 therefore, incorrect. 



The proposition should read : 



Right side. Left side. 



Upper -|- middle lobe = upper lobe. 



Lower -|- cardiac lobe = lower lobe. 



4. The active principle in changing and modifying the archi- 

 tecture of the lung is not the pulmonary artery (Aeby), but ;;//- 



