Joseph Marshall Flint 11 
indicates his belief in the final solution of the question through embryo- 
logical investigations. An interesting parallel, in a more limited way, 
might be drawn between the effects of Aeby’s stimulating paper and 
the energetic investigations in the field of experimental biology which 
followed the annunciation of Weismann’s views on heredity. 
Aeby abandoned entirely any idea of dichotomy and substituted in its 
place a strict monopodial explanation of the arrangement of the branches 
of the bronchial tree. Each lung, according to this author, possesses a 
stem bronchus which forms its axis and leaves the lung at the hilum to 
fuse with its mate on the opposite side as they join the trachea. Of great 
importance is the relationship which the pulmonary vessels, especially the 
arteries, bear to the bronchial tree. The veins run in front of the 
bronchi, the arteries behind, as the latter are forced in leaving the heart 
to cross over the large air passages to reach their place. This crossing 
occurs near the upper end of the stem bronchus and divides the tree into 
two distinct segments of different importance. These are termed epar- 
terial and hyparterial, according to their position with reference to the 
point where the pulmonary arteries cross the bronchi. 
The arrangement of lateral bronchi is throughout typical and regular. 
Few occur in the eparterial while most are in the hyparterial zone. The 
former may be absent, but the latter are always present. The hyparterial 
systems of both lungs are symmetrical, but the eparterial systems, on the 
contrary, are ordinarily asymmetrical. The hyparterial bronchi always 
appear in two series, a dorsal and a ventral, which usually alternate and 
have their origin from the stem bronchus relatively close to each other, 
leaving the greater portion of the large bronchus free from branches. 
This forms then the angle of a three-sided prism from which the two 
series of lateral bronchi extend into the adjacent space bounded by the 
chest wall. The dorsal bronchi are shorter. The lateral bronchi give up 
some of their branches to the stem bronchus, a process which may be fol- 
lowed, according to Aeby, step by step, with the greatest clearness. These 
wander medialwards and finally cover the previously naked portion of the 
stem bronchus with dorsal and ventral accessory bronchi. These either 
remain close to the parent stem or else wander downwards. ‘Their de- 
velopment begins usually quite far down the left lung, while in the right, 
they appear higher up and often produce a special bronchus supplying 
the Lobus infracardiacus known as the Bronchus cardiacus. 
Eparterial bronchi are always single and never give off accessory 
branches. They arise from the stem bronchus at a point midway between 
the sites of origin of the lateral bronchi and divide generally into dorsal 
and ventral branches. One, especially the left, or both may be absent, 
