464 SANGUIFEROUS SYSTEM. 



branchia on the left side, is transmitted to a capacious thin 

 auricle and a thick muscular ventricle (22. h.) on the same 

 side, to be distributed through the system by the great 

 anterior and posterior aortal branches. The auric ulo- ventri- 

 cular orifice is here protected, as usual, with two very distinct 

 semilunar folds, in the position of the mitral valves of mam- 

 malia. The aorta immediately divides into several large 

 trunks which proceed forwards to the oesophagus and head, 

 upwards to the large muciparous follicles and the mantle, 

 and backwards to the digestive and the generative organs. 

 The branchial tufts of the doris being placed around the anus 

 and protected in the same cavity of the mantle, the heart is 

 here situated on the median and posterior part of the back, 

 and receives the aerated blood from the gills into a crescentic 

 auricle disposed around the rectum, nearly as the ventricle of 

 conchifera. The short round muscular ventricle is here placed 

 anteriorly to the auricle, and gives origin to a large median 

 aortal trunk which advances forwards along the back to the 

 head, sending off large branches to the liver, the intestine, 

 the genital organs, and other parts in its course. In the pul- 

 monated gasteropods, as the helix, lymncea, and other genera, 

 and in many which breathe by gills as the aplysia, bullaea, 

 and others, the respiratory organs, and consequently also the 

 heart, are placed on the right side of the body. The arte- 

 rialised blood of the aplysia (Fig. 121.) collected from the 

 numerous laminae of the gills (121. p.) under the right margin 

 of the mantle, is received into a capacious auricle (121. g.) 

 and thence into a strong muscular pyriform ventricle, (121. r.) 

 like that of many fishes. The bulbus arteriosus (121. r. h.) 

 is of a lengthened form like that of plagiostome fishes, and 

 when injected or inflated appears transversely sacculated, 

 which induced Cuvier to believe that it was surrounded with 

 lateral arterial loops communicating with its cavity and des- 

 tined to secrete the fluid of the pericardium. The aorta gives 

 off a large hepatic (121. o.) and gastric (121. h.) artery, and 

 then directs its course downwards to advance and distribute 

 its branches along the ventral part of the body. The dila- 

 table and sacculated portion of the aorta, which appears some- 

 what analogous to the numerous transverse valvular folds in 

 the bulbus arteriosus of plagiostome fishes, here extends be- 

 yond the origins of the hepatic and gastric arteries. 



