The American journal of anatomy . sial and the lateral moieties of the subbronchial sac atthis stage of development. In the preceding sketches (exceptfigure 18) the mesial moiety of the interclavicular sac has notbeen shown chiefly because the sketches were executed beforewe had learned to look for the two moieties of this sac, and,further, the aspect from which the specimens were drawn did notbring the mesial moiety into view. The diagram (fig. 20) was made from observations by re-flected as well as by transmitted light and the connections of theair-sacs with the bronchi are indicated. On the
The American journal of anatomy . sial and the lateral moieties of the subbronchial sac atthis stage of development. In the preceding sketches (exceptfigure 18) the mesial moiety of the interclavicular sac has notbeen shown chiefly because the sketches were executed beforewe had learned to look for the two moieties of this sac, and,further, the aspect from which the specimens were drawn did notbring the mesial moiety into view. The diagram (fig. 20) was made from observations by re-flected as well as by transmitted light and the connections of theair-sacs with the bronchi are indicated. On the lateral borderof the lung is seen the lateral moiety {) of the interclavic- THE EMBRYOLOGY OF THE BIRD S LUNG 469 ular sac connected with the transverse branch of the first ento-bronchus. The mesial moiety {) arises in connectionwith the anterior intermediate air-sac, and these two have acommon opening into the third entobronchus. The distal endof the mesial moiety is forked and partly encircles the Fig. 19 J^i^so( lion cxpoMiiii, (lu i iglit lung and adjacent viscera of an embryoat the close of the tenth day (jt incubation. Shows indentations of the ribs andrecurrent bronchi from the abdominal and posterior intermediate air-sacs. In embryos 10| days old the air-sacs exhibit the very interest-ing condition (figs. 40 and 47) of recurrent bronchi springingfrom all the air-sacs except the cervical (which never has any),and, further, that the interclavicular sac is derived from twomoieties on each lung. These are the lateral and mesial moietiesalready referred to. Details in reference to the union of these 470 WILLIAM A. LOCY AND OLOF LARSELL four moieties to form the single interclavicular sac of the adultare brought out in section 3 of this paper. The significant external features of the lung are now estab-lished and subsequent changes show, chiefly, increase in size ofthe lungs, a relatively larger increase of dimensions of the air-sacs and the de
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