OF THE OPHIDIAl^S m GENEKAL. 
23 
possible volume, but of which the parts are susceptible of 
an extraordinary enlargement, so as to permit serpents to 
swallow the large animals intended by nature for their 
sustenance. Now, to answer this end, the bony case of 
the heads of serpents does not form, as in the greatest 
number of the other vertebrata, an immoveable mass ; but 
the component parts are so united together, that all of 
them, except those enclosing the brain, are susceptible of 
a greater or less movement, and generally in different 
directions. This is particularly the case with the bones 
which, entering into the formation of the lower jaw, give 
configuration to the head. The development of the 
panites^ their mode of attachment, their mobility, which 
depend; on not being fixed to the cranium by their inferior 
extremities ; in short, the structure of the lower jaw, the 
two branches of which, instead of being united by a sym- 
physis, are banded together by elastic ligaments, and are 
thus susceptible of considerable separation ; these are the 
circumstances which principally contribute to the enormous 
enlargement of the mouths of serpents. The total want 
of feet necessarily implies the absence ’ of certain solid 
parts, such as the sternum, the pelvis, &c., which unite 
the limbs to the trunk ; the ribs free, and hence enjoying 
an uniform mobility, contribute to the enlargement of the 
intestinal cavity, and to that change of the form of the 
trunk so visible in the different positions of the serpent in 
running, in swimming, or in climbing. To obey these 
various movements, the general integuments are divided 
into numerous compartments, which form so many articu- 
lations, parallel to the parts they cover ; the scales which 
form the articulations, on the lower part of the animal, 
are usually, larger than the rest, and perform the office of 
feet ; the ribs are attached to the lateral margin of the 
internal face of these plates. The naked space of skin 
between the scales is more considerable than in all other 
reptiles ; and at the throat, this naked skin, in order to 
accommodate itself to the separation of the jawbones, 
occurs in the form of a longitudinal fosse, called the gular 
fissure. By this structure of the general integuments, 
these tunics, contracted in a state of repose, accommodate 
