Volltext: The Cyclopaedia of Anatomy and Physiology, vol 1: A-Dea (1)

really is, on account of its deep position and 
the overlapping of the kidney, E. As it gets 
beyond this part it is seen to dilate. Two veins, 
corresponding to the ventz iliacæ of Quadrupeds, 
(m, m,) return the blood in part to the tail, and 
join the vena cava near the kidneys. The vein 
corresponding to the caudal or sacro-median of 
Quadrupeds is not a simple vessel, but a 
plexus, which is surrounded and protected by 
the inferior spinous processes ; it is seen at f. 
A venous plexus from the intestinal canal (g) 
terminates in the right iliac vein, which is 
larger than the left, and thus establishes a com¬ 
munication between it and the portal system. 
h shows a muscular vein, and i the termination 
of a hypogastric plexus. 
The more important plexuses which commu¬ 
nicate with the iliac veins are, first, the perito¬ 
neal plexus (Z), which in older individuals, and 
especially at the season of sexual excitement, is 
much more considerable than is here repre¬ 
sented; and secondly, the iliac or psoadic 
plexus (k,k), which forms an immense reser¬ 
voir of venous blood. It is situated between 
the under surface of the depressors of the tail, 
which represent the psoas muscles, and the 
peritoneum, reaching from behind the lower 
extremity of the kidney to the posterior end of 
the abdomen, and forming a mass of closely 
interwoven veins, of an inch or more in thick¬ 
ness, and serving to bring the subcutaneous 
veins of the posterior part of the body into 
communication with the posterior vena cava. 
This plexus is fed, if we may use the ex¬ 
pression, by a, an inferior vein; b, a lateral; 
and c, a superior vein of the tail, which unite 
to form an ischiadic sub-plexus, d. Laterally 
the iliac plexus receives from five to seven 
veins, which return the blood from the dorsal 
and lateral parietes of the abdomen, and pierce 
the lateral abdominal muscles to join the plexus 
at e, e. On its internal or mesial edge the iliac 
plexus communicates by many and wide aper¬ 
tures with the iliac vein. At the anterior part 
of the abdomen the inferior cava receives the 
plexus phrenicus, o, o. 
The condition of the venous system above 
described, while it is admirably adapted to the 
mode and sphere of existence of the Cetaceans, 
presents a beautiful instance of that co-ordinate 
analogy to the condition of the veins in the 
embryo of the higher Mammals, which is ex¬ 
hibited in the general form of the animals 
composing this the lowest order of the class.] 
Organs of Respiration.—The organs and 
all the essential phenomena of respiration are 
the same in the Cetaceans as in the other 
Mammals. They have been made the subject 
of but few observations. 
[In the Dugong the lungs are of a very elon¬ 
gated and flattened form, resembling those 
which Daubenton has figured of the Manatee. 
They are, as Sir Everard Home has observed, 
one-fourth the length of the animal; those 
from the animal, eight feet long, which he re¬ 
ceived from Sir Stamford Raffles, measuring 
two feet. They are convex posteriorly or on 
the dorsal aspect, flattened on the opposite 
side, and along this surface the principal 
branches of the bronchi can be seen through 
the serous covering. The upper end of each 
lung is obtuse, thick, and narrow ; they gradu¬ 
ally become flatter towards the lower extremity, 
the margin of which is rounded. 
The whole surface of these lungs presents an 
appearance somewhat similar to that of the 
Turtle ( Chelonia Mydas), in consequence of 
the large size of the superficial air-cells, which 
are a line in diameter (a, a, fig. 268.) The 
great extent of the lungs down the back, and 
the high division of the trachea, and consequent 
length of the bronchi, are further instances of 
this resemblance. 
Fig. 267. 
Cartilages of the bronchus of the Dugong. 
The cartilages of the bronchial tubes are 
continued spirally into one another (fig. 267) : 
the pulmonary artery lies to the outer side of 
the bronchus and is deeper seated; the pulmo¬ 
nary vein to the inner side, and is superficially 
situated. The principal branch of the bron¬ 
chus (b, fig. 268) runs down near the inner 
margin of the lung, and continues distinct to 
within four inches of the end ; it then divides 
into smaller branches; the larger ramifications 
are given off from its outer side, c, c. In all 
the branches the cartilaginous rings continue 
distinct and strong till their diameter is con¬ 
tracted to one or two lines ; the rings passing 
irregularly into each other as in the main 
trunks. The lining membrane of the air- 
tubes is thrown into longitudinal rugae, in¬ 
dicating their dilatability. We have before 
mentioned the large size of the pulmonary 
artery : in this respect, as well as in the 
structure of the lung, the Dugong manifests 
a greater similarity to the reptile than the 
Porpoise does. In this animal the air-cells in 
no part of the lung exceed a sixth part of the 
size of the superficial ones in the Dugong; and


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