Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Todd, Robert Bentley
marked by Nitzsch, may be considered a rudi¬ 
ment of the left lung. The right, and in this 
case sole, pulmonary sac is placed immediately 
below the spine ; it extends posteriorly as far as 
the region of the kidneys, and in the Coluber 
natrix is from five to seven inches long, and 
from one-half to three-quarters of an inch 
broad. Its parietes are thickest at the point 
where the rings of the trachea cease, where 
it is covered externally by a fibrous layer, 
and lined internally by a fine lattice-like net- 
workof vessels. More posteriorly the pa¬ 
rietes become gradually thinner, and at last 
are merely membranous, giving to the whole 
organ still more of the appearance of a swim¬ 
ming bladder. In the slow-worm (Anguis 
fragilis) there are two lungs, nearly as in 
the salamander, though the left is still con¬ 
siderably smaller than the right. The respi¬ 
ratory motion here, as in the amphibia, is 
unassisted by a diaphragm, and is principally 
effected by the ribs and abdominal muscles. 
In Saurian reptiles the respiratory organs 
are generally formed pretty nearly as in 
tortoises. The larynx is tolerably simple, 
without vocal ligaments, and in the chame¬ 
leon is furnished with a small sac-shaped 
appendage: in most Saurians, e.g. the croco¬ 
dile, it opens by a longitudinal fissure; but 
in the chameleon by a transverse one. This 
opening is always unconnected, being placed 
far back, and somewhat covered by the pos¬ 
terior edge of the tongue in the crocodile, but 
in other species lying more forwards. Many 
of the species belonging to this order have 
the power of emitting a sound by the volun¬ 
tary tension of the rima glottidis, as is known 
to be particularly the case in the Geckos, 
where the tongue, which can be thrown 
back like that of the frog, appears to serve 
as an epiglottis. In the larynx we already 
find, particularly in the crocodile, a large 
pointed anterior cartilaginous lamina as a 
rudiment of the thyroid cartilage. The tra¬ 
chea and bronchi are nearly the same as in 
tortoises, i. e. composed of almost completely 
circular cartilaginous rings. In the Gecko the 
trachea is particularly wide and somewhat 
flattened. The lungs likewise form double 
cellular sacs, extending downwards far behind 
the liver; whilst in the crocodile, on the con¬ 
trary, they remain above the liver, and, conse¬ 
quently, more in the thorax, resembling very 
nearly, both in their shape and position, the 
lungs of birds. In the chameleon, the lungs 
are furnished inferiorly with peculiar finger- 
shaped appendages. Respiration is effected 
by the thoracic ribs and their muscles, without 
the assistance of a diaphragm. 
The Circulation of the Blood.—In Tortoises 
the heart is situated immediately above the 
liver, and close behind the abdominal scutum : 
it consists of two auricles and a ventricle, the 
latter being divided into several communicating 
cells, and presenting a broad circular de¬ 
pression, having likewise strong muscular 
parietes, and being connected at its inferior 
obtuse extremity by means of a tendinous 
ligament to the pericardium, as is the case 
in many fishes. The auricles are extremely 
capacious, eit her of them being very nearly equal 
Fig. 221. 
Heart of the Tortoise. (After Bojanus.') 
The ventricle opened in front, the left aorta laid 
open, and a bristle placed in the pulmonary artery. 
in size to the ventricle : they are divided by 
a septum, which, however, is perforated in 
the Testudo scorpioides. The right receives 
the blood of the body by means of the venae 
cavae, whilst the oxygenized blood from the 
pulmonary veins enters the left by a fissure¬ 
like valvular orifice. The internal arrangement 
of the ventricle varies somewhat in different 
instances ; in some, e. g. the Testudo græca, 
it is little more than a simple cavity, rendered 
irregular by the projecting bundles of fibres of 
its parietes ; in others, on the contrary, e. g., 
the T. imbricata, these fibres are so very 
prominent, and appear to divide the cavity so 
completely into several cells, that Mery was 
induced to admit the existence of a ventricle 
for the pulmonary artery and aorta, in ad¬ 
dition to a right and left ventricle. Whether 
the cavity, however, be simple or compli¬ 
cated, the course of the blood through the 
heart is always such, that the pulmonary blood 
enters at the left side, is mixed with the blood 
of the venae cavae rather towards the back 
part of the heart, and then passes on the 
right side into the aorta, and anteriorly into 
the pulmonary arteries. 
The principal arterial trunks form a circle 
Fig. 222. 
Heart of the Tortoise. (After Bojanus.) 
The ventricle laid open in front, the pulmonary 
artery slit up, a bristle placed behind a columna 
camea, which forms an imperfect septum. 
round the oesophagus, which we must consider 
as a repetition of the branchial arteries. The 
aorta, which in the T. imbricata is furnished 
with two semilunar valves, arises double from 
x 2


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