ORGANS OF CROCODILIANS. 639 
be closed by valves, and the eyes by transparent third eyelids, and 
the ears by movable flaps, so that the head can be comfortably im- 
mersed ; a flat tongue is fixed to the floor of the mouth, and the 
cavity of the mouth is bounded behind by two soft transverse mem- 
branes, which, meeting when the reptile is drowning its prey, pre- 
vent water rushing down the gullet ; the posterior opening of the nostrils 
is situated at the very back of the mouth, and when the booty is being 
drowned, the Crocodilian keeps the tip of its snout above water, the 
glottis is pushed forward to meet the posterior nares, a complete channel 
for the passage of air is thus established, and respiration can go on un- 
impeded. For their shore work the Crocodilians prefer the darkness, 
but they often float basking in the sun, with only the tip of the snout 
and the ridge of the back éxposed. 
Glands with a secretion which smells like musk are usually developed 
on the margin of the lower jaw, at the side of the cloacal aperture, 
and on the posterior margins of the dorsal scutes. The musky odour 
is very strong during the pairing 
season, and when the animals are 
attacked. ; 
In connection with the muscular 
system, the presence of what is 
often called an incipient diaphragm 
between the thoracic and the ab- 
dominal cavity is of interest. 
The brain seems very small in 
relation to the size of the skull. 
The eyes are provided with a 
third eyelid, as in most Reptiles, 
Birds, and Mammals; there are 
large lachrymal glands, but there 
is no special deceitfulness about 
“*crocodile’s tears.” Fic. 352.—Half of the pelvic 
The ears open by horizontal girdle of a young crocodile. 
slits, over which lies a flap of 
skin; three Eustachian passages— 
one median and one on each side— 
open into the mouth behind the posterior nares. 
The nostrils alsa. can be closed, and, as we have already noticed, 
their internal opening lies at the back of the mouth. 
The stomach suggests a ‘bird’s gizzard, for it has strong muscular 
walls, and its pyloric end is twisted upward so as to lie near the cardiac 
art. 
The heart is four-chambered, the septum between the ventricles being 
complete, as in Birds and Mammals. Butas the dorsal aorta is formed 
from the union of a left aortic arch containing venous blood, and a 
right aortic arch containing arterial blood, the blood which is driven to 
many parts of the body is ‘‘mixed blood,” ze. blood partly venous, 
partly arterial, with some of its red blood corpuscles carrying heemo- 
globin and others oxyhzmoglobin. At the roots of the two aortic 
arches there is a minute communication between them—the foramen 
Panizze. 
7i,, lium; af, acetabulum; /s., 
ischium ; P., pubis or epipubis. 
