MANTLE-CAVITY 



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from side to side. Contraction of its muscles causes 

 flattening of the floor, and thus enlarges the cavity, 

 causing an inrush of air through the pulmonary 

 aperture. On relaxation of the muscles the floor 

 resumes its previous convex shape, diminishing the 

 size of the cavity and effecting expiration. 



By alternate contraction and relaxation of the 

 floor of the mantle-cavity the air is continually 

 renewed, and the cavity thus becomes a true lung. 



PC 



FIG. 22. Helix pomatia. Dissection from the right side to show the 

 mantle-cavity and organs in relation with it. The arrow passes 

 through the pulmonary aperture into the mantle-cavity. (A. M. M.) 



A, auricle. B, anus. C, collar. D, dorsal body-wall forming the floor of 

 the mantle-cavity. E, eye. F, foot. G, genital aperture. H, groove leading 

 to genital aperture. K, kidney. L, lip. P, pulmonary vein. PA, pulmonary 

 aperture^ PC, pulmonary or mantle-cavity. PV, pulmonary vessels in roof 

 of mantle-cavity. P V, cut ends of pulmonary vessels. R, rectum. S, inferior 

 tentacle. T, superior tentacle. U, ureter. V, ventricle. 



B. The Organs in relation with the Mantle-cavity. 

 1. The pericardial cavity and heart. 



a. The pericardial cavity, which has already been seen 

 from the exterior, is oval, thin-walled, and half 

 an inch or more in length. It lies in the roof of 



