IN THE PERENNIBRANCHIATE BATRACHIA. 215 
distinct auricular chamber, which communicates with the ventricle by an oblong orifice, 
situated close to, but separated from, the corresponding orifice of the great auricle of 
the veins of the body. 
In the present communication the heart of the Sir. lacertina is selected for more 
immediate consideration, as this species, in presenting a combination of but one pair 
of extremities with persistent external branchie, recedes furthest from the Batrachian 
type of structure, and might be supposed to approximate Fishes most closely in the con- 
struction of the central organ of circulation. 
The heart of the Sir. lacertina is of an oblong figure, situated immediately behind the 
branchie in the middle line of the body between the two fore legs and surrounded by 
a strong fibrous pericardium, which is smooth and glistening on the inner surface, as in 
Fishes, adheres by the whole of its exterior surface to the surrounding parts, and is 
defended on the ventral aspect by the expanded cartilaginous coracoid bones. The 
length of the pericardium in a specimen two feet in length was two inches, its breadth 
three fourths of an inch. 
The heart when viewed externally seems composed of a membranous sinus, a large 
muscular fimbriated auricle, a ventricle, and an elongated bulbus arteriosus. 
The venous sinus is situated at the posterior part of the pericardium. The great 
inferior cava terminates in this sinus by two orifices, separated from each other by a 
membranous septum'!, which extends a little way into the sinus, and terminates in a 
concave edge anteriorly ; on either side of this free margin of the septum there is an 
orifice, one of the right, the other of the left, superior cava”, between which the com- 
mon trunk of the pulmonary veins* is seen adhering by a small part of its posterior sur- 
face to the parietes of the sinus, but not terminating there. 
If the lower part of the auricle be carefully laid open in the transverse direction, a 
small cavity will be exposed distinct from the rest of the auricle, and above the sinus, 
into which the trunk of the pulmonary veins opens. This distinct compartment‘, which 
is analogous to the left auricle, and is here situated to the left side of the ventricle, 
communicates with the ventricle by an oblong aperture close to that by which the right 
auricle opens into the ventricle, the two apertures being separated by a transverse band 
which forms the point of attachment to the simple membranous auriculo-ventricular 
valves. This division of the auricle into two cavities, one for the systemic the other 
for the pulmonic blood, would scarcely be suspected to exist upon an external view of 
the heart, on account of the remarkable fimbriated structure of the auricles, arising 
from numerous indentations of varying extent: the deepest of these clefts is, however, 
that which separates the appendix of the left from that of the right auricle. The inter- 
nal surface of both auricles presents numerous delicate muscular ridges, which decus- 
sate in various directions: the subdivided elongated cylindrical pouches continued from 
the margin of the auricle present a manifest analogy with the remarkable structure of 
te. Big. 2. Pl. xxxi. * 6, b. Fig. 3. 3m. Figg. 2. & 3. +e. Big. 2. 
