GENERAL NOTES ON SNAKES. 631 
The bifid, mobile, retractile tongue ts a specialised organ of 
touch. tn the mouth there is often a poison gland, which is a 
specialised salivary gland. 
There are many peculiarities in the skeleton. The numerous 
vertebre are all procelous. 
The brain has only ten nerves. 
The heart is three-chambered, the ventricular septum being 
incomplete, as in all Reptiles except Crocodilians. 
There is a transverse cloacal aperture. In the males a 
double saccular and spiny copulatory organ ts eversible from 
the cloaca. 
Snakes ave widely distributed, but are most abundant in 
the tropics. 
ri 
Fic. 346.—Snake’s head.—After Nuhn. 
dv., Poison fangs; ., sheath of fang; 2. tongue ;. 77., muscles ot 
tongue. 
General notes on snakes, — Snakes, . especially when 
poisonous, are often brightly coloured. The scales on the 
head form large plates, and those on the ventral surface are 
transverse shields. In many cases there are odoriferous 
glands near the cloacal aperture. 
The muscular system is very highly developed, and the 
limbless serpent, Owen says, “can outclimb the monkey, 
outswim the fish, outleap the zebra, outwrestle the athlete, 
and crush the tiger.” 
The vertebrae are very numerous, some pythons having 
four hundred; they are proccelous, and are distinguishable 
only into a pre-caudal and caudal series. 
All the pre caudal vertebree except the first—the atlas— 
have associated ribs, which are movably articulated, and 
