EPARTERIAL BRONCHIAL SYSTEM. 131 



a. The " eparterial" bronchus, if unilateral, is always on 



the right side. 



b. The *' cardiac " bronchus is always on the right side. 



EXAMINATION OF TYPES. 



We may profitably begin our consideration of the mammalian 

 bronchial tree by examining seriatim a number of selected types, 

 subsequently comparing the members of the entire series, in 

 their probable phylogenetic relation to each other, and draw 

 our general conclusions from such comparison. 



For reasons, which will be stated later, and which induce us 

 to regard the form as the representative of the primitive mam- 

 malian lung, we begin with the type described by Aeby as 

 ** Bronchial Tree without Eparterial Bronchus," the complete 

 bilateral hyparterial type. 



I. Hystrix cristata — European Porcupine. 



Corrosion of bronchial system and pulmonary artery. Co- 

 lumbia University Museum, No. 413. PL XV. 



The caudal end of the trachea enlarges to a capacious pen- 

 tagonal bulla or lacuna, slightly compressed dorso-ventrally. 



The bronchi, hyparterial in their derivation on both sides and 

 perfectly symmetrical, arise from the tracheal bulla as two main 

 trunks, cephalic and caudal (PI. XV, A, A, B, B). Each trunk 

 divides, in a nearly dichotomous manner, into two nearly equal 

 secondary branches (PI. XV, A', A" , B' , B^'), which in turn 

 give off, by monopodic division, tertiary branches. 



1. Cephalic Trunk (PI. XV, A, A). 



a. Apical Branch (/J ') passes to the anterior portion of 



each lung. 



b. Lateral Branch (^A") supplies the central (middle) por- 



tion of each lung. 



2. Caudal Trunk (PI. XV, B, B). Both medial and 



lateral secondary branches [B' and B") ramify in the 

 posterior portion of the lung. 



