ANATOMY OF THE OPHIDIA. 391 
There is an apex about 18 mm. long, reaching to the 61st g.; it 
is above and to the right of the trachea, to which it is closely 
adherent posteriorly, the terminal 6 mm. only being free. The 
lumen of the apex communicates directly with the lung and is 
not set off by a restriction. The respiratory tissue ceases rather 
abruptly at about the 80th g. ; its disappearance is not accompanied 
by the gradual change in size and shape of the air-cells so 
frequently seen. 
The left lung, 86 mm. long, extends from the 62nd to the 
80th g., and is the largest recorded in a Colubrine snake. The 
base is attached to the right side of the ventral surface of the 
right lung; it is 8 mm. long and corresponds to the 64th and 
65th g. Though adherent to the right lung there is no direct 
communication between the two, the interpulmonary septum being 
imperforate. Just posterior to the base the diameter of the left 
lung is 7 mm. There is a free apex, 12 mm. long, extending 
forward nearly to the auriculo-ventricular septum; it is in 
relation with the left side of the pericardium, to which it is 
closely adherent. The posterior end of the lung extends 6 mm. 
beyond the anterior tip of the liver. The left lung is closely 
_ adherent to the inferior vena cava, and hides this vessel when the 
ecelum is opened from beneath. The left bronchus is merely a 
little bulge on the ventral side of the trachea 4 mm. anterior to 
its termination. There is no trace of a left intrapulmonary pro- 
longation or fibrous band. The lung is lined throughout with 
regular air-cells ; these are larger and more shallow than in the 
right lung. 
The pulmonary artery courses along the right lateral edge of 
the right lung. Its principal branches are as follows: No. I, a 
minute one to the ventral surface of the apex. No. IT, a large 
one which is at the level of the middle of the apex and winds 
around to its outer side and then turns to the dorsal surface of 
the lung. No. III enters the lung at the base of the apex. 
No. IV, very small, crosses to the right over the middle of the 
ventral surface of the isthmus joining the two lungs. No. V,a 
large branch, which runs along the posterior border of the isthmus 
and divides, sending several twigs to the right lung and a small 
branch to the left lung. The branches beyond are too irregular 
to describe in detail; some enter the lung direct, some wind 
around the right side to the dorsal surface, and one large one 
crosses the ventral surface and is distributed to the left side. 
The right aorta gives the impression of being a branch of the 
vertebral artery *. It arises from the right side and is less than 
ove half the calibre of that artery. It flows directly to the 
rear, forming an acute angle with the vertebral. It crosses to 
the left aorta and upon reaching that vessel at the 64th g. it 
courses alongside to the 68th g. before joining to form the 
dorsal aorta. There is a single intercostal branch which enters 
to the left of the median line at the 61st g. 
* Quite as in Zamenis flagelliformis, Beddard, P. Z.5. 1904, vol. i. p. 388. 
