630 REPTILIA. 
structure. For the external shape is in great part an adapta- 
tion to the mode of life, to the habit of creeping through 
crevices or among obstacles. But the limblessness of 
serpents is not a merely superficial abortion; there is no 
pectoral girdle nor sternum, and never more than a hint of 
a pelvis. 
GENERAL CHARACTERS.— Zhe skin ts covered with scales, 
and the outermost epidermal layer ts periodically shed in 
a continuous slough. 
There are never any hints of anterior appendages, girdles, 
Fic. 344.—-Anterior view of Fie. 345.—Posterior view of 
Python’s vertebra. Python’s vertebra. 
N.SP., neural spine ; ZS., ZYZor ZA., zygantrum, a double cavity 
sphene (a projecting wedge); PR.Z., for the zygosphene; P7.Z., post- 
pre-zygapophysis (mooth articular zygapophysis (smooth articular 
surface seen from above); &., surface seen from below); 7.P., 
articulation-surface for a rib; HY., transverse process ; C., centrum. 
hypapophysis. 
sternum, or episternum,; but in pythons, boas, and a few 
others, there are rudiments of a pelvis, and even small clawed 
structures which represent hind-legs. 
The mouth is expansible; maxilla, palatines, pterygotds, 
and guadrates are movable; and the rami of the mandible 
are connected only by elastic ligament. The teeth are fused to 
the jaws ; there are no movable eyelids. Snakes have no 
external ear openings nor drum, nor tympanic cavity, nor 
Eustachian tube. The nostrils le near the tip of the 
head, 
