PULMONARY EVOLUTION IN MAMMALIA 1t3 
sions. In one marine chelonian of undetermined genus he de- 
scribes the pulmonary artery as crossing the stembronchus high 
up, before any lateral bronchi arise, and continuing caudad on 
its dorso-lateral aspect, giving branches from each side to the 
bronchial derivatives. The distribution of the tree is therefore 
entirely hyparterial. Hesser (22), as quoted from a_ personal 
communication by Flint (21, p. 22), was unable to find an epar- 
terial bronchus or a bronchus which corresponded to it in his 
extensive work on the reptilian lung. 
My own material convinces me that in the reptile the archeal 
hyparterial type of bronchial organization prevails uniformly as 
soon as the phyletic stages are reached in which the definition is 
at all applicable. The simpler lacertilian forms show the begin- 
ning of a more complex organization in the cranial segment of 
the lung. This increases in the higher types, reaching its greatest 
development in the marine chelonia and in the crocodilia. 
Figure 3 shows a corrosion preparation of the right lung of 
Aspidonectes spinifer (Columbia University Morph. Mus. no. 
1931) from the ventral aspect. In the cranial segment the stem- 
bronchus is encrusted with a rich efflorescence of secondary and 
tertiary bronchial buds. In the rest of its extent the stembron- 
chus gives origin to a series of regularly disposed lateral and 
medial primary derivatives with secondary budding. The pul- 
monary artery enters the cranial lung-pole close to the stem- 
bronchus and on its dorso-lateral aspect. The bronchial dis- 
tribution is altogether hyparterial down to the minute details. 
There is nowhere any indication of eparterial bronchial budding 
in the mammalian meaning of the term. This is typical of the 
more highly developed reptilian lungs, as far as my material and 
observation extend. I cannot therefore regard the possession of 
a bilateral eparterial pulmonary organization by a mammal as 
in any way referable phyletically to its reptilian ancestry. On 
the contrary, I look upon it as a distinctly new mammalian acqui- 
sition (ef. infra, p. 175). 
The lung of the Aplacentalia places itself on the basis of the 
early ontogeny and of the immediately succeeding stages in direct 
line with the ancestral reptilian type (cf. p. 192), but this evi- 
THE AMERICAN JOURNAL OF ANATOMY, VOL. 27, No. 2 
