Page 42 - Reptiles & Dinosaurs (Britannica Illustrated Science Library)

38 REPTILES: BACKGROUND REPTILES AND DINOSAURS 39

Internal Organs A Question GROWTH OF

THE SCALES
he anatomy of reptiles enables them to live on land. Thanks to their dry, scaly skin and their of Skin 100 Epidermis Dermis
excretion of uric acid instead of urea, they minimize water loss. The heart distributes blood in a The absence of extremities
and the friction produced
T double circuit. Crocodiles were the first vertebrates to have a four-chambered heart; the during movement give snakes THE NUMBER OF TIMES 1 The dermal layer is found
below the epidermis.
A VIPER SHEDS ITS SKIN
separation of the ventricles is incomplete in all other reptiles. The lungs, developed beyond those of the ability to slide and to shed OVER ITS LIFETIME.
amphibians, contribute to cardiac efficiency by allowing for greater exchange of gases. their skin in one motion. Other
reptiles must shed their skin by
tearing it off in
pieces. Reptiles Differentiation takes place
shed their skin 2 during dermal cell growth..
regularly and
continue to do
16 to 20 feet (5-6 m) SKIN Jugular Neck PLACEMENT OF THE SCALES so even in the last
Reptiles have chromatophores Region years of their lives.
that modify their color to a Transverse Longitudinal NEW SKIN The epidermis secretes
Lines
Lines
small degree. Two unique is smooth and bright. 3
Weight: more than 1 ton traits of crocodiles are that large amounts of keratin.
the skin on the head has
NILE CROCODILE Anus CORAL SNAKE OLD SKIN
Crocodylus niloticus glands that regulate the is fragile. It
body's ionic balance, and the Micrurus altirostris rips easily.
Diet Carnivorous cloaca has glands that secrete The flanks and the stomach are It is characterized by its smooth Melanophores Osteoderms The new scales overlap
Longevity 45 years in the wild and substances crucial for mating lighter and shinier than the and brightly colored scales. Flexible Joint 4 each other and cover
80 years in captivity and defense. dorsal surface. the skin.
EYES OLFACTORY MESENCEPHALON LUNGS STOMACH DORSAL AORTA SPLEEN TESTICLES KIDNEYS
have telescopic vision, BULB MEDULLA contain air sacs contains rocks transports Lobuled. Their Metanephric. The DOUBLE CAUDAL
ideal for locating prey. BRAIN CEREBELLUM OBLONGATA called alveoli. that help break oxygenated blood ducts empty in ureters empty in CREST
down food. throughout the body. the cloaca. the cloaca.

MOUTH
is closed by strong
muscles. The rear portion
contains a membrane TEETH
that prevents water from retain prey. They do CLOACA SIMPLE CAUDAL
entering while the animal not chew but cut prey Shared opening of the CREST
is diving. into pieces, which are PITUITARY excretory, reproductive,
swallowed whole. GLAND and digestive ducts
64 to 68 TEETH
ESOPHAGUS COLON
Circulatory System TRACHEA HEART LIVER SMALL BREATHING Abdominal The liver compresses
INTESTINE
the lungs.
Muscles
Nile crocodiles have double 1 EXHALING
Internal organs are
circulation. A minor circuit brings THE HEART compressed. This, in
deoxygenated blood to the lungs and The flow patterns inside the heart prevent the turn, compresses the
transports oxygenated blood from them, mixing of pulmonary and systemic blood. Respiratory System lungs and causes
and a major circuit transports the MAMMAL REPTILE AMPHIBIAN them to expel air. Air is
oxygenated blood to the rest of the body 4 Chambers 3 Chambers 3 Chambers is completely pulmonary. Most reptiles expelled.
and returns deoxygenated blood to the possess a pair of functional lungs, with
heart. Reptile hearts have two auricles BLOOD CIRCULATION the exception of snakes, which have only one
(atria) and a single ventricle, which is An ample and efficient functional lung. Body-wall muscles generate the 2 INHALING The pressure difference causes the
partially divided by an incomplete ventricle network of blood pressure differences necessary to circulate air The pelvic bones rotate lungs to expand and take in air.
partition. vessels extends through the airways from the nasal cavities to downward, the abdomen
stretches, and the
throughout the bodies the pulmonary alveoli. muscles cause the lungs
of reptiles. to expand.