. The American journal of anatomy. e Sinus venosus, leaving the arteries to developfrom behind. That is to say, with the increasing size of the right andleft stem bronchi and the consequent enlargement of the capillary plexua Joseph Marshall Flint 63 about them, it is natural, with the venous outlet already estalilished onthe ventral side of the sacs, that the capillaries on the dorsal side shouldenlarge into arteries. Furthermore, after its origin and partial separa-tion from the oesophagus, the terminal part of the entire pulmonaryapparatus extends somewhat ventralwards from the head gut mak
. The American journal of anatomy. e Sinus venosus, leaving the arteries to developfrom behind. That is to say, with the increasing size of the right andleft stem bronchi and the consequent enlargement of the capillary plexua Joseph Marshall Flint 63 about them, it is natural, with the venous outlet already estalilished onthe ventral side of the sacs, that the capillaries on the dorsal side shouldenlarge into arteries. Furthermore, after its origin and partial separa-tion from the oesophagus, the terminal part of the entire pulmonaryapparatus extends somewhat ventralwards from the head gut making itadditionally easier for the arteries to form on the dorsal than the ventral-surface of the anlage. These factors are responsible for the course,which the arteries and veins take with reference to the bronchial tree,while the asymmetry of the stem bronchi appears to cause the chief dif-ference in the course of the arteries on the two sides. It is, further-more, possible that some of this irregularity is also due to the medial. Schema A. Schema to show the origin of the relations of the pulmonary vessels to thelungs. LA = Lung anlage. AP = Arteria pulmonalis. YP^Vena pulmon-alis. = Site of origin of Lateral 1 the eparterial bronchus. L. 2 ^ Siteof origin of Lateral 2, the first bronchus in the hyparterial region. L =Liver anlage. bending of the right artery in preparation for its transfer from theright to the left pulmonary arch according to the suggestion of Bremer,although in Bremers descriptions, with which my specimens agree, thisactual transfer is made at a much later period, and I am accordinglyinclined to minimize the possible influence of this factor. It is alsoworthy of note that we have no crossing of the bronchi by the arteriesin the sense of Aeby. As they run down, they gradually turn dorsal-wards to take up a position behind the primitive sacs and are lost in thecapillary plexus, which surrounds them. The pulmonary vein, scarcely 6-1 The Development of the
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