The document summarizes lung ventilation in different reptile groups. It states that while most reptiles rely solely on lung ventilation, lizards lack a diaphragm and instead use chest muscles. Some lizard species can also use throat muscles in a process called buccal pumping to force air into their lungs. In contrast, crocodilians have a muscular diaphragm similar to mammals that pulls the pelvis back to allow lung expansion during breathing.

1. Respiratory System in Reptiles
All reptiles breathe through their lungs. The reptile lung
has a much greater surface area for the exchange of
gases than the lungs of amphibians. Many reptiles’ lungs
have little sacs called alveoli, across which gas is
exchanged. This makes their lungs much more efficient
than those of amphibians. Lung ventilation is done
differently in each main reptile group.
In squamates (scaled reptiles such as lizards and snakes),
the lungs are ventilated almost exclusively by
the muscles of the chest wall. These same muscles are
used during movement, so most squamates have to hold
their breath while exerting themselves (running fast).

2. Reptiles depend entirely on their lungs for respiration.
Lizards do not have a diaphragm; instead, their
chest muscles move the chest wall, which inflates and
deflates the lungs.
A few lizard species use their throat muscles to “gulp” air
in a process called buccal pumping (a process also used
by amphibians). Animals that use the “buccal pump”
method take in air through the nose and move the floor
of their mouth or throat up and down in a way that
makes the animal look as if it were gulping air. When its
mouth is full of air, the lizard will push the air down into
the lungs. The nostrils are then closed, the glottis
opened, and the floor of mouth is raised, forcing the air
into the lungs for gas exchange. To deflate the lungs, the
process is reversed. Mammals, in contrast, use their
thoracic diaphragm to inflate and deflate the lungs more
directly.
.

3. Crocodilians actually have a muscular diaphragm that is
similar to the mammalian diaphragm. The difference in
crocodilians is that the muscles for their diaphragm pull
part of the pelvis back, which brings the liver down and
frees space for the lungs to expand.
Unlike other vertebrates, most reptiles lack a secondary
palate, which is a division between the nasal cavity and
the oral cavity. Therefore, reptiles must hold their breath
while swallowing. Crocodilians have evolved a bony
secondary palate that allows them to
continue breathing while remaining submerged.
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