98 Messrs. Hancock Embleton on the Anatomy of 
attached to the skin, and by means of these attachments the 
heart and great vessels are secured in their position. The heart 
and vessels thus inclosed lie free in the cavity, which they fill 
when fully distended with blood. The heart and pericardium lie 
above all the other viscera, and immediately beneath the skin of 
the back, on the median line, and just behind the anterior third 
of the body. 
In J^. coronata and those species which have the branchiae 
similarly arranged, they lie between the second and third clumps. 
They form during life a manifest elliptical elevation, more or 
less transparent, and in which the pulsations may be seen and 
counted. 
On opening a specimen preserved in spirits, the auricle, fig. 2 h, 
is seen at the posterior part of the pericardium, of a cruciform 
figure, resulting from the union of two large trunks of veins 'p'p, 
coming from the sides of the body with one, from the posterior 
part, lying along the median line ; the anterior limb of the cross 
is formed by the contracted portion of the auricle r, where it goes 
forwards to open into the ventricle a. The walls of the auricle 
are quite smooth and polished externally, and within are formed 
of a very fine but wide meshed reticulation of delicate muscular 
bundles which are continued upon the greater venous trunks. 
At the anterior contracted part is placed a valvular apparatus, 
fig. 3 c, the auriculo-ventricular, to guard the ventricular opening 
which is on the under surface of the heart. 
The auriculo-ventricular valve consists of two flaps continuous 
at their bases with the walls of the ventricle and prolonged into 
its cavity, having their ends attenuated and free. They are placed 
one under and the other over the opening, the former being 
longer than the latter. They are broad and strong, and when 
brought together they will effectually close the opening. The 
opening is wide, and the auricle is attached to its margin at the 
bases of the valvular flaps. 
The ventricle a, much smaller than the auricle, is of a pyriform 
shape, with its apex anteriorly. Its walls are considerably thicker 
and more fleshy than those of the auricle, and its cavity displays 
very numerous, strong and bold projecting carnese columnae, some 
of which are attached to the bases and outer surfaces of the valves 
at both orifices. The interior of the ventricle from its high de- 
velopment reminds us forcibly of ,fhat of animals much higher 
in the scale. The upper half of the organ is much thicker than 
the under, owing to the superior number and strength of its 
fleshy columns. The muscular fibres of the auricle and ventricle 
arc devoid of transverse striae ; they are minute, simply granular 
and rounded. 
A valve, the aortic, fig. 3 d, is placed at the anterior or pointed 
