466 SANGUIFEROUS SYSTEM. 



branchiae, and, thus aerated, is conveyed to the single auricle, 

 and ventricle to be distributed to all parts of the body. The 

 thin, transparent, and tough pericardium inclosing the heart 

 of the clio borealiS) as shown by Eschricht, lies towards the 

 right and posterior part of the abdominal cavity, with its 

 broadest part behind, and its apex directed forwards. The 

 ventricle, about half a line in length, is in form of a trun- 

 cated triangular pyramid, with rounded Angles, as in many 

 gasteropods and fishes ; its parietes are thick and its cavity 

 small, it gives origin to the aorta at its tapering anterior 

 apex, and communicates posteriorly with the thin membra- 

 nous auricle placed at its base. The aorta, on perforating 

 the pericardium, continues its course forwards, sending 

 branches, as in the gasteropods, to the liver and genital 

 organs ; and advancing towards the head, gives off minute 

 arteries to the neck and to the large muscular lateral fins. 

 The heart lies also on the right side of the abdominal cavity 

 in the hyalea and pneumodermon, and consists of a single 

 systemic auricle and ventricle, inclosed in a thin transparent 

 pericardium, as in the clio and in most of the cephalous mol- 

 lusca ; and the arterialised blood is returned from the respi- 

 ratory organs by the branchial veins to the auricle and ven- 

 tricle, to be distributed through the body. 



The bilateral symmetry of the cephalopods, so conspicuous 

 in their osseous and muscular systems, in their motor and 

 sensitive columns and nerves, and in their organs of sense, 

 is not less obvious in their respiratory and circulating appa- 

 ratus, and forms a closer link of connexion between them 

 and the fishes and other vertebrated classes, than is observed 

 in the inferior mollusca. The auricle in the naked cephalo- 

 pods, as in the conchifera, is divided into two similar and 

 separate muscular cavities, which here receive, as in fishes, 

 the venous blood of the system before it is transmitted to 

 the respiratory organs. The ventricle is single and systemic, 

 as in the other molluscous classes, median in its position, 

 placed with the auricles in the middle of the abdominal 

 cavity, and receives the arterialized blood from the branchiae, 

 to be transmitted by an anterior and a posterior aortal trunk 

 through the body. The venous blood collected from the 

 capillaries of the arms and suckers, is returned by the inter- 

 brachial veins to an irregular, transverse, circular trunk 



