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 off 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. 
