Joseph Marshall Flint 79 
the Lobus superior, Lobus medius, Lobus infracardiacus, and Lobus in- 
ferior, while Lateral 2 and the stem bronchus produce the Lobus superior 
and Lobus inferior on the left. At 10 mm. the swelling over L. 1 is 
practically in the same lateral plane as L. 2, while at 12.5 mm. it is 
crowded slightly dorsalwards by the further growth of the latter. 
In a pig 13.5 mm. long (Fig. 17), the characteristics of the lobe 
formation are intensified. On the right side, the upper lobe containing 
Lateral 1 is pushed still more dorsalwards, while the middle lobe con- 
taining Lateral 2 is, at the same time, forced shghtly ventralwards by 
the antagonism in the growth of their two main bronchi. The Lobus 
infracardiacus, containing Ventral 2, extends downwards and medial- 
wards, while the lower lobe extends more caudalwards and is now, 
through its whole extent, distinctly prismatic in cross-section. On the 
Text E1q@. 18. 
Text Fic. 18. Outline drawing of the lungs of an emtryo pig 14.5 mm. 
long. A. Ventral view. B. Dorsal view. Designation of lobes as in Fig. 16. 
left side, the Lobus superior, owing to its more unobstructed environ- 
ment, extends somewhat higher than its homologue, the Lobus medius, on 
the right side. The Lobus inferior is not quite so large or well devel- 
oped as the corresponding right lobe. The primary fissures between the 
several lobes have deepened and now extend well into the substance of 
the lung. With the division of Lateral 1 and Lateral 2 on each side, the 
secondary branches also raise secondary projections on these surfaces of 
the lobes between which are slight secondary furrows. Similarly the 
Lobus inferior on each side shows slight swellings limited by shallow 
grooves over L. 3 and L. 4. In the pig, these swellings and grooves, 
however, under ordinary circumstances, never lead to a separation of 
the lung substance into extra lobes. 
Fig. 18 shows the lungs of an embryo 14.5 mm. long. The Lobus 
