48 



along a line going obliquely from right to left (i.e., the 

 long axis of the ventricle), and representing Avhat was 

 the main or aiitero-posterior axis of the ventricle in 

 ancestral Molluscs. 



On opening this chamber of tlie lieart, the interwoven 

 muscle hbres, which form much of its wall, are seen 

 radiating fr(nn the thickened margin of the auriculo- 

 ventricular aperture, which is situated near the middle 

 of its antero-dorsal side. The aperture is guarded by 

 two valvular flaps which project into the ventricle cavity. 



The main aorta and its posterior branch, the visceral 

 artery, diverge in opposite directions right from the 

 origin, and as they run parallel to, and in close connection 

 with, the ventricle wall, we get an appearance as of a 

 third chamber of the heart. This appearance is 

 emphasised by the fact that the beginnings of the aorta 

 and visceral artery are swollen, and that this pseudo- 

 chamber resembles the ventricle in general characters. 

 The heart of Patelht was described as three-chambered 

 by Wegmann, who gave the name " Intermediate 

 Chamber " to that which is here called " Ventricle," and 

 the name "Ventricle" to the pseiulo-chamber or aoitic 

 bulb formed by the swollen arterial bases. AVegmann's 

 determination of parts Avouhl make the limpet's lieart 

 practically sui generis, and would remove the genus very 

 far from the Rhipidoglossa, and even from its nearei' allies. 

 The present account, on the other hand, shows the essential 

 similarity between Patella and the other Docoglossa in 

 this respect, and agrees with the conclusiojis of llaller and 

 of Bout an. The aperture between the ventricle and the 

 aortic bulb is guarded by a valvular Hap which projects 

 into the cavity of the latter. 



Arteries. — The Aorta, of which the origin has jusi 

 been descriltcd. runs to Ihe right cud of the pericardium. 



