ON THE ANATOMY OF THE OPHIDIA. 379 
25. Further Contributions to the Anatomy of the Ophidia. 
By Josnpa C. THompson, Surgeon, U.S. Navy *. 
Received October 22, 1913: Read April 21, 1914. | 
INDEX. 
Anatomy : Page 
Methods employed ...........0.....0.......... 879 
List of species examined ....................... 9380 
Meruops EMPLOYED. 
A routine procedure is needed for recording and correlating 
observations nade on the anatomy of serpents. In comparative 
anatomical studies of mammals, the position of an organ is given 
in terms of its relation to other viscera. With animals of a 
compact build this is amply sufficient ; with serpents on the other 
hand, owing to their attenuated bodies, it is not adequate to state 
that one organ lies posteriorly to another. This drawing out of 
the body is accompanied by much variation as to the relative 
lengths of different organs and their distances apart. For 
example, the tip of the liver may be situated the distance of a 
dozen vertebre behind the apex of the heart, with a thick-walled 
right lung filling the space between them, or it may overlap the 
apex of the heart by several millimetres, and the lung be a mere 
air-sac dorsal to the liver. The length of certain organs varies to 
a degree unknown in any other Order. For example, the right 
lung may terminate a few millimetres posterior to the end of the 
liver, or extend nearly to the cloaca. 
If the gastrostege level at which the various structures occur 
is recorded, one may obtain data satisfactory for comparing 
different species or for determining the range of variation in 
a series. ‘lake for example the data relating to ZThammnophis 
ordinoides: the apex of the heart is recorded as being at the 26th, 
the anterior tip of the liver at the 70th, and the posterior end at 
the 86th gastrostege. It may be seen at a glance that the liver 
is nine gastrosteges posterior to the heart and that it is of a 
definite length, extending over thirty-five shields. For com- 
paring series it will be found of advantage to reduce the records 
to a percentage. In each case the number of gastrosteges in the 
specimen is to be taken as the base. 
Returning to Z. ordinoides: the number of gastrosteges in an 
example of that species is 157, and the position of the heart or liver 
in terms of its distance down the spinal column is as follows :— 
Heart apex 16°6 per cent.; liver tip 22°3 per cent.; liver end 
44-6 per cent. Behind the posterior pair of geneials there are 
usually one or two pairs of small gular shields ; these are followed 
by from one to three shields in the median line which increase 
* Communicated by Dr. F. E. Beppsarp, M.A., F.R.S.,-F.Z.8. : 
+ To avoid frequent repetition the term gastrostege will be abbreviated to “ g 
? 
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