98 Messrs. Hancock and Embleton on the Anatomy of Eolis. 



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 E. 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 b, 

 is seen at the posterior part of the pericardium, of a cruciform 

 figure, resulting from the union of two large trunks of veins pp, 

 coming from the sides of the body with one, q, 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 columnar, 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 that 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 

 are devoid of transverse strise ; they are minute, simply granular 

 and rounded. 



A valve, the aortic, fig. 3 d, is placed at the anterior or pointed 



