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1894.] The Classification of Snakes. 839 
the rudimental lung is not a constant character. I found it 
in one Heterodon platyrhinus and not in another; it is present 
in Conophis pulcher, but absent in C. sumichrastii. 
The rudimental lung is often concealed from view and diffi- 
cult to discover.. The best test of its presence is the foramen 
which connects it with the trachea, which will generally be 
found piercing the cartilage of the latter near the apex of the 
heart. The rudimental organ may then be found by inserting 
a bristle, and observing its destination through the more or 
less transparent tissues. In but one instance have I found a 
rudimental lung without a connecting foramen, viz, in the 
Mexican Ficimia olivacea. On the other hand, the foramen 
may terminate in a small blind sac. 
The pulmonary characters may be determined without 
much dissection. The position of the heart must be first as- 
certained, and a longitudinal median incision made in the 
abdominal wall In all forms except the Epanodonta and 
Catodonta, the trachea will be found passing to the left side of 
the heart, and entering the lung near its apex. By splitting 
the trachea, not too near its abdominal border, on turning the 
free margin upwards as the snake lies on its back, the foramen 
bronchiale will be seen and its lumen can be explored. The 
trachea is concealed by the cesophagus, which must be drawn 
to the left side of the body in order to make the examination. 
The examination of the tracheal lung requires the division 
of the abdominal wall farther towards the head. 
The tracheal lung greatly extends the surface available for 
blood aération. This is necessary to snakes for the reason that 
the huge masses of food which they ingest, so compress the 
true lung that another organ is necessary. Most snakes 
whether they have a tracheal lung or not, have the pulmonary 
organ greatly elongated, so that while one portion is compressed 
by the contents of the alimentary canal, another part is free to 
function. The tracheal lung enables the snake to inflate the 
anterior part of the body. This is conspicuous in the true 
venomous sp lypha) Inthesame way Heterodon 
inflates its huge diverticulum. In the marine water snakes 
Chersydrus and the Hydrophidae, these organs serve as floats. 
