I.] THE FROG. 43 



a. The (esophagus ; a thick walled tube lying at or near 

 the middle of the whole section. 



b. The lungs; thin walled spongy sacs (tubular in sec- 

 tion) right and left of a. 



c. The liver; occupying the greater portion of the 

 pleuro-peritoneal cavity and lying immediately below 

 a. and b. 



d. The heart; situated in the middle ventral line. 



e. The neural canal and central nervous system; rela- 

 tively much larger than in Sect. i. 



f. The body-wall; in part inflected, giving rise to a 

 sheet of muscle (so-called diaphragm) which is 

 attached, on opposite sides, to the oesophagus. 



g. The aorta; here paired {aortic arches). 



h. The pericardmm ; a double-walled sac enclosing 

 the heart, and related to it as is the pleuro-peri- 

 toneal membrane to the body-wall and its con- 

 tained viscera. 

 i. The pleuro-peritoneal membrane. (Cf. generally 

 with previous section.) Note that having sus- 

 pended the organs above-named, it passes round 

 the pericardium, giving rise to a fold {falciform 

 ligament) which is reflected on to the body-wall 

 below, there being thus formed a septum which 

 completely subdivides the pleuro-peritoneal cavity, 

 in this region, into two. 

 Its special folds are: 

 a. The ligamentum latum; suspending the lung to 



the oesophagus. 

 j3. The lesser omentum; passing between the oeso- 

 phagus and liver in the middle line, 



