In the Urodela
the scapula ossifies, and its ossification may
be prolonged into the coracoid and precoracoid, but there is
never more than one osseous mass. The clavicle is not developed.
, the Derotremata
, and Salamandridea
coracoids are received into grooves of the anterolateral edges
of a cartilaginous sternum.
The pectoral arch of the Labyrinthodonts seems to have
possessed representatives of clavicles in the lateral thoracic
shields. The structure of the rest of the arch is not clear, but
ossified coraco-scapular pieces seem to have existed.
In the Batrachia
, the coraco-scapular cartilages are sometimes,
as in the common Frog, firmly united in the middle
line, and send forward a median process, which becomes ossified,
and is the omosternum
(Fig. 57, o.st.
). Behind the coracoids
articulate with a well-developed sternum (st
ossifications arising on either side of the glenoidal cavity represent
the scapula (sc
.) and the coracoid (cr
.), and the upper
moiety of the scapula may be distinctly ossified as a suprascapula
|Fig. 57. - The sternum and pectoral arches of a Frog, seen from above. The left supra
scapula is removed: sc, scapula; s.sc, supra-scapula; p. sc, prescapular process; cr.,
coracoid; e-cr., epicoracoid; cr.f., coracoid fontanelle. The bar which bounds this in
front is the precoracoid, and bears the clavicle: o.st. omosternum; st., sternum; x.st xiphisternum.
The coracoid is divided by a large membranous
space ov fontanelle
into a proper coracoid (cr.
), which lies
behind the fontanelle
; a persistently cartilaginous epicoracoid
), which bounds it internally; and a precoracoid
limits it in front. Closely applied to the precoracoid is an
ossification in membrane, which represents the clavicle.
The pelvic arch is attached (except in Proteus
) to the extremity
of the sacral rib. An iliac ossification is always developed; an ischial, in all but Proteus
. The pubis does not appear
to be regularly represented by a distinct ossification. In
the applied flat faces of the expanded ventral
divisions of the pelvic arch coalesce into a disk.
In the genus Amphiuma
, the limbs have each either two
or three digits. In Siren
, the anterior limbs, which alone
exist, are three-or four-toed. In Proteus
, the anterior limbs
are tridactyle, the posterior didactyle. Menobranchus
tetradactyle feet, while in the other Urodela
the anterior limbs
are tetradactyle, the posterior pentadactyle. The Batrachia
have four digits, with or without a rudiment of another, in the
fore-limb, and five in the hind-limb. In the perennibranchiate Urodela
, the cartilages of the carpus and tarsus, which, except
, present little deviation from the typical number
and arrangement (Fig. 11, p. 32), remain unossified; in the
, and in the Batrachia
, they are for the most