Bauhaus-Universität Weimar

The Cyclopaedia of Anatomy and Physiology, vol. 4: Pla [corr.: Ple] - Wri
Todd, Robert Bentley
column, receiving at the point where it begins 
to take this direction from before backwards 
the left branch of the right aorta, which forms 
a loop in front of it. From the convexity of 
this loop arises the left carotid. The two 
other branches of the right aorta wind back¬ 
wards, and join together in a similar manner 
upon the right side of the neck, forming two 
loops placed one in front of the other. The 
right carotid arises from the convexity of the 
loop. The subclavians are given off from each 
aorta a little before their union, except in 
crocodiles and the iguana, where they are 
both derived from the right aorta. The 
common trunk formed by the union of the 
two aortæ, which takes place just beyond the 
apex of the heart, gives off in succession 
numerous pairs of intercostal arteries. It 
sends, moreover, shortly after its commence¬ 
ment, an artery to the oesophagus, and 
subsequently a small branch to the liver; 
further backwards it gives off an artery 
which soon divides into two branches : of 
these the anterior supplies the stomach, the 
spleen, the pancreas, and the duodenum ; 
the posterior, which represents the anterior 
mesenteric, is appropriated to the intestinal 
canal. The aortic trunk then gives off in 
succession the lumbar, the spermatic, the pos¬ 
terior-mesenteric, which supplies the rectum, 
and the renal, which are given off thus late 
because the kidneys are situated very far back 
in the abdominal cavity : lastly, it gives origin 
to the iliacs and the middle sacral arteries. 
The last-mentioned vessel may fairly be re¬ 
garded as a continuation of the aortic trunk, 
from which the iliacs seem to be mere 
branches ; a circumstance which is owing to 
the excessive proportions of the tail when 
compared with the extremities. 
In the Ophidian reptiles, the absence of 
limbs, the existence commonly of a single 
lung, and the extremely slender and elongated 
form of the body, concur to render the distri¬ 
bution of the arterial trunks very simple 
throughout this order. These trunks, as in 
the Chelonians and Saurians, are three in 
number. Their first divisions, instead of being 
double and symmetrical, are reduced to single 
trunks. This is the case, for example, with 
the pulmonary artery in those serpents that 
possess but one lung, and also with the com¬ 
mon carotid, and the vertebral in the entire 
It is from the convexity of the right aorta, 
and very near its origin, that the above 
branches, destined to supply blood to the 
head and neck, are derived. 
The right aorta then winds backwards, 
passes above the oesophagus, and then running 
obliquely inwards and backwards, it joins the 
left aorta at a little distance beyond the apex 
of the heart. 
The right aorta gives off, a little after its ori¬ 
gin, a small artery that supplies a small round 
glandular-looking mass situated in front of 
the base of the heart, and subsequently to 
another similar body of elongated form, situ¬ 
ated beneath the jugular vein. It then gives 
off the common carotid, which is single in all 
the Ophidia. A third artery is given off a 
little further on, which is the common trunk 
of the vertebral and anterior intercostals. No 
other important artery is given off' by the 
right aorta, and when it joins the left aorta 
its diameter is very small, so that the greater 
portion of the blood that this vessel receives 
from the heart is supplied to the organs 
which are situated in front of that viscus : it 
might therefore be properly named the carotid 
The carotid artery runs obliquely towards 
the left side, and advances forward, closely 
connected to the left jugular vein, between the 
trachea and the oesophagus, and at length is 
situated beneath the latter. It gives off a 
great number of small branches to these parts, 
and near the head divides into several small 
arteries, which represent both the external 
and internal carotids. 
When the right aorta approaches the verte¬ 
bral column, it gives off, as stated above, a 
considerable branch, which supplies thé place 
both of the vertebral arteries and the anterior 
common intercostals. This artery advances 
beneath the vertebral column, giving off 
branches on both sides, opposite each inter¬ 
costal space, both to the muscles and to the 
vertebrae of the region which it traverses, and 
only enters the vertebral column close to the 
head. This vertebral and intercostal artery 
likewise gives off recurrent branches, which 
furnish intercostal vessels behind its point of 
The left aorta runs upwards, backwards, 
and to the left side : passes beneath the oeso¬ 
phagus, and afterwards beneath the lung until 
it reaches beyond the apex of the heart, 
where it receives the right aorta, and con¬ 
tinues its course backwards. It continually 
gives off branches corresponding to the inter¬ 
costals and the visceral arteries : those which 
furnish the stomach, the liver, and the pul¬ 
monary sac or sacs, are given off successively 
from the aorta in its course backwards, so 
that there is nothing like caeliac axis. Nearly 
opposite the pylorus it gives off the anterior 
mesenteric, which runs parallel to the intestine 
for half its length, to which it constantly 
furnishes branches. Further backwards the 
intestinal canal receives in succession three 
other small branches from the aorta, which 
gives off as it runs backwards arterial branches 
to the kidneys, ovaries, and other viscera. 
Arrived at the termination of the abdomen, 
it passes on beneath the vertebrae of the tail, 
in which it becomes gradually expended. 
Organs of Respiration. — In several species 
of Lizards the cavity of the fauces is much 
enlarged by an expansion of the skin in front 
of the larynx (fig. 216, d.). These laryngeal 
sacs, as they are called, appear to be recep¬ 
tacles for air rather than food ; for, although 
not connected with the larynx, they are ex¬ 
traordinarily distended in rage, &c. 
Before the termination of the trachea, both 
in the Coluber natri.v and thiringicus, there is 
a small blind depression, which, as was first re-


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