The young
reptile loses them during its embryonic life--as man and all the
mammals and birds do to-day--and issues from the egg a purely
lung-breathing creature. A richer blood now courses through the
arteries, nourishing the brain and nerves as well as the muscles.
The superfluous tissue of the gill-structures is used in the
improvement of the ear and mouth-parts; a process that had begun
in the Amphibian. The body is raised up higher from the ground,
on firmer limbs; the ribs and the shoulder and pelvic bones-- the
saddles by which the weight of the body is adjusted between the
limbs and the backbone--are strengthened and improved. Finally,
two important organs for the protection and nurture of the embryo
(the amnion and the allantois) make their appearance for the
first time in the reptile. In grade of organisation the reptile
is really nearer to the bird than it is to the salamander.
Yet these Permian reptiles are so generalised in character and so
primitive in structure that they point back unmistakably to an
Amphibian ancestry. The actual line of descent is obscure. When
the reptiles first appear in the rocks, they are already divided
into widely different groups, and must have been evolved some
time before.
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