PLATE LV. 

 SECOND ANTERIOR VIEW OF THORAX. 



In this plate the lungs have been drawn aside to uncover the pericardium ; this 

 has been opened to show the position of the heart mid great vessels. 



Aeby ' opposes the idea that the bronchi divide dichotomously as they pass into the 

 lungs, and states that each tube passes in as an axial stem in the lung substance, 

 giving off branches in definite directions. These branches can be divided into 

 primary, and secondary or accessory branches which are probably only subdivisions of 

 the primary that have become implanted on the axial trunks. The primary branches 

 are in two sets : those given off in front of the pulmonary artery eparterial ; and those 

 given off behind hyparterial, the latter arise from the outer surface of the stem bronchus 

 and pass in two directions, some ventrally and some dorsally. The pulmonary artery 

 as it passes backwards lies on the outer surface of the axial bronchus, between the two 

 . Small and more irregular branches arise on the inner surface of the axial 

 bronchus ; these ore the accessory bronchi. Thus the arrangement is more bipinnate 

 than dichotomous. 



If the human bronchi be examined it will be seen that the right one gives off a branch 

 above 2 the place where the pulmonary artery crosses it, this is not represented on the 

 left side, it is the eparterial bronchus : and thus Aeby supposes that the lobe of the 

 lung to which it is distributed is also absent on the left side, and that the middle lobe of 

 the right lung represents the whole of the upper lobe on the left ; for all the rest of the 

 bronchi come off below the crossing of the pulmonary artery, and hence are hyparterial. 

 His has shown that in the development of the human lung, the right bronchus possesses 

 at first only two buds which correspond to the eparterial and first ventral hyparterial 

 bronchi ; while the left bronchus has but one such bud, which corresponds to the first 

 ventral hyparterial bronchus. The branching on the left side is more profuse than on 

 the right, an especially strong dorsal branch being given off which runs upwards. This 

 is unrepresented on the right side and compensates for the loss of the eparterial bronchus. 

 In the sheep and ox the eparterial bronchus of the right upper lobe springs from the 

 trachea, and this condition has been met with in the human subject. In some animals 

 eparterial branches spring from both bronchi and supply corresponding lobes in the 

 two lungs. 



1 Aeby, Der Bronchialbnum der S&ugethiere und tits MenscJten. Leipzig, 1887. 

 ' In quadrupeds the term in front of the pulmonary artery corresponds to above in the human 

 subject, and behind to be Ion: 



