SPECIAL ANATOMY. 235 



Chapter viii. — of the respiratory and circulatory- 

 apparatus. 



The lung of the Terrestrial Gasteropoda is a simple 

 cavity, with an orifice communicating with the exterior, 

 upon the right side of the body. The surface of this 

 pulmonary cavity in part of its extent, and more parti- 

 cularly near the pulmonary orifice, is covered by a close 

 intertexture of blood-vessels. The blood of the body is 

 conveyed directly to the lungs by two principal vessels, 

 the pulmonary arteries, which join the capillary rete of 

 the pulmonary surface. From this rete passes ofi" the 

 pulmonary vein to the heart, which is systemic, and con- 

 sists of an auricle and ventricle. The auricle receives 

 the pulmonary vein ; from the ventricle passes off the 

 aorta, to be distributed throughout the body. 



Limax. The pulmonary cavity is situated beneath 

 the mantle, and has nearly the same size and form. It 

 is separated from the visceral cavity by the muscular 

 peritoneum, but contains the rectum, renal organ, and 

 heart. The pulmonary orifice is situated at the antero- 

 inferior edge of the mantle, on the right side of the body. 

 When open it appears round ; it is closed by means of 

 circular, muscular fibres. The pulmonary rete is princi- 

 pally displayed upon the roof of the cavity, and from it 

 converge three principal trunks, to form the pulmonary 

 vein which passes to the auricle of the heart. 



