ANATOMY OF THE OPHIDIA. 40 1 
It begins at the glottis and rapidly widens to comprise 50 per cent. 
of the circumference of the tube; at the 42nd gastrostege it has 
increased in width to 66 per cent., and just before the heart it is 
fully 80 per cent. ‘The cartilaginous rings are markedly thin and 
weak ; towards the end of the trachea they lie along the dorsal 
and left segment of the tube. The trachea for its entire length 
is destitute of air-cells. It gives every indication of fiiling all 
the available space along its course. There is no line of demar- 
cation to show where it ends and the lung begins. The alveolar 
tissue of the left lung is thin; it begins very gradually at about 
the level of the auriculo-ventricular septum, and continues 
to the 116th g.; from this point to the 128th g. there are 
a few large irregular air-cells before the anangious portion 
begins. There is no free apex and no rudimentary left lung. 
The heart apex is at the 91st g., and the tip of the liver at the 
101st. Gastrosteges 272. There are 13 rows of scales from the 
neck to the level of the 265th g.; at this point the median row 
is suppressed, leaving 12 rows. 
Causus RHOMBEATUS Lichtenstein. 
Specomen.— Brit. Mus. Nat. Hist. Ex. No.’13-lla@, Fort Hall, 
British Hast Africa. Adult male. 
The trachea increases in diameter and occupies a large part of 
the cervical region ; its walls are almost entirely formed by the 
membrane. The tracheal membrane begins on the left side at 
the level of the glottis; it rapidly widens, and after a few 
millimetres becomes lined with pulmonary tissue which in no 
respect differs from that found in a normal lung. 
The cartilaginous portion at the origin almost surrounds the 
tube, being incomplete only on the left ; at the 12th gastrostege 
it becomes ventral and forms a small U-shaped gutter, 1-5 mm. 
in diameter; as it approaches the heart it gradually flattens out 
and is continued onto the anangious portion as a band. This 
intrapulmonary bronchus ends at the 65th g.; it is not a mere 
strip of fibrous tissue but a flat band of similar structure 
to the tracheal wall, with the alternate sections of cartilage and 
connecting membrane. The right lung has a very scanty lining 
of pulmonary tissue ; thickly-set air-cells cease on the ventral 
surface of the tracheal membrane at the 32nd g., dorsally they 
are continued a little further; from this on to the heart apex 
there are large oblong cells extending along each side of the 
tracheal band ; on the lateral walls of the lung these alter to an 
irregular shallow honeycomb structure; posterior to the heart 
apex the lung is a simple air-sac, with the remnant of the 
bronchus along its ventral wall. The left lung is completely 
suppressed. 
The heart is situated principally to the right of the median 
line; it is rotated on its long axis until the right auricle is 
nearly dorsal to the left. 
The pulmonary artery divides 3 mm. from its origin into 
