DR, T. CANTOR ON PELAGIC SERPENTS, 305 
The spinous processes of the dorsal column are small, whereas those of the caudal 
vertebre are very large and compressed, gradually diminishing in size towards the point 
of the tail. 
The greater number of terrestrial serpents are covered with scales, the points of which 
are free, acting like stoppers, which, by catching the nearest objects, prevent retrograde 
motion ; the water offers no such obstacles, and we find the pelagic serpents in general 
covered with small broad scales, with their whole circumference attached to the skin, and 
either slightly keeled, or having an elevation in the centre, like the umbo of a shield. 
Of the internal organs, the respiratory offer the most striking differences from those 
of the terrestrial serpents. The trachea consists of a long gradually-widening cylinder, 
with numerous short cartilaginous rings, which extend as far backwards as the liver, 
without dividing into bronchi. At some distance before the heart the trachea becomes 
cellular, and from this place commences the single lung, which is a long narrow cylin- 
der, in several places widened into spacious sacs, which again assume the contracted 
form at the posterior extremity of the liver, continuing thus through the entire length 
of the abdominal cavity, and is fixed by a short round ligament near the anus. The 
cancellated structure of the parietes is continued throughout, although the cancelli de- 
crease in size in the posterior part of the lung. The great developement of the latter 
organ’ bespeaks its high importance, and it has two distinct functions to perform, the 
one of which is to serve as the organ of respiration, or as a reservoir for atmospheric 
air, which, when the mouth and the nostrils are closed, allows the oxidation of the 
blood to be carried on a considerable time under the surface of the water, by the vibra- 
tion of the cilia which line the whole interior of this cavity, and thus enables the ser- 
pent to go to great depths in search of food. Secondly, the lung filled with air floats 
the body, particularly when the food is swallowed, and the specific gravity increased by 
the weight of a foreign body ; the part situated behind the stomach becomes, by the 
pressure of the filled stomach, an isolated sac,—in fact an organ analogous to the air- 
vessel in fishes. 
The esophagus is funnel-shaped, widening into a large bulb, communicating by a 
short cylinder with the pyriform stomach. The intestines, after forming a number of 
circumvolutions, terminate by a short straight portion, entering the spacious rectum. 
The liver is short, divided by a longitudinal furrow into two lobes, the interior of which 
is again divided by a short transverse furrow. In the pelagic serpents the situation 
of this organ is remarkable, as being in immediate contact with the heart. In the 
Hydrophis striata and gracilis, Schlegel, the hepatic, cystic, and pancreatic ducts enter 
jointly the duodenum, but in the H. schistosa, Schlegel, the hepatic duct divides into a 
number of little branches, which terminate in the cystic duct to form the ductus com- 
' Next to the pelagic serpents, the lungs are most developed in the aquatic genera, Achrocordus, Chersydrus, 
Homalopsis, and Cerberus, all of which, notwithstanding their being innocuous, are, in habits and anatomical 
structure, closely allied to the pelagic serpents. 
VOL. IIl.—PART Iv, 2s 
