THE COELOM, DIGESTIVE, AND RESPIRATORY SYSTEMS 173 



vertebrates. It does this and so becomes an independent sac, the pericardial sac. This 

 process of the splitting of the pericardial sac from the body wall is aided by the invasion forward 

 of the pleuroperitoneal cavity. The heart contained in the pericardial sac descends posteriorly, 

 the pleuroperitoneal cavity at the same time advancing anteriorly. The pericardial sac may 

 be thought of as sliding posteriorly ventral to the ventral wall of the pleuroperitoneal cavity. 

 The pericardial sac thus comes to lie ventral to the anterior part of the pleuroperitoneal cavity. 

 The posterior wall of the pericardial sac is still the anterior face of the transverse septum, the 

 posterior face of the latter as in lower forms being placed between the pericardial sac and the 

 liver. The transverse septum thus in the turtle forms part of the partition between the peri- 

 cardial and the pleuroperitoneal cavities, the remainder of the partition being composed of the 

 rest of the parietal pericardium, which is now the pericardial sac. These matters will be better 

 understood by reference to Figure 45^ and C. 



2. The viscera and their mesenteries. — With the bone scissors cut away 

 the margins of the carapace on each side between fore and hind limbs so as to 

 gain easy access to the pleuroperitoneal cavity. Masses of fat, greenish-yellow 

 material, will be found in various places and may be removed. Lift up the edges 

 of the cut already made in the peritoneum, widening this if necessary, and look 

 inside. Identify in the anterior part of the pleuroperitoneal cavity the large 

 brown liver lying on each side of the heart. Posterior to the liver are the coils 

 of the intestine. In female specimens the ovaries containing eggs of various 

 sizes are conspicuous objects in the lateral and posterior part of the pleuroperito- 

 neal cavity. Running alongside each ovary is the coiled oviduct. Just in front 

 of the pelvic girdle is the large bilobed urinary bladder. 



The liver consists of right and left lobes whose lateral margins curve dorsally 

 to fit the curves of the carapace. The pericardial sac rests in a depression 

 between the two lobes. The latter are united by a narrow bridge passing dorsal 

 to the heart. Posterior to the heart the liver is united to the parietal peritoneum 

 by very short mesenteries corresponding to the falciform ligament of other verte- 

 brates. In these mesenteries the ventral abdominal veins leave the peritoneum 

 and pass into the liver. Trace the parietal peritoneum anteriorly from this 

 region. It passes along the dorsal face of the pericardial sac, to which it is 

 inseparably fused. This compound membrane between the heart and liver is 

 the transverse septum, which has assumed an oblique position, owing to the 

 descent of the heart (Fig. 45) . The ventral (original anterior) face of the septum 

 is as before, part of the wall of the pericardial cavity; the dorsal (original pos- 

 terior) face forms part of the parietal peritoneum. The liver is as usual attached 

 to the transverse septum by the coronary ligament. Continue to trace the 

 parietal peritoneum to the anterior end of the pleuroperitoneal cavity. On 

 the posterior face of the pectoral girdle it turns dorsally and passes to the carapace 

 of which it forms the inner lining. Similarly trace the parietal peritoneum pos- 

 teriorly by lifting the posterior cut edge of the membrane. It curves dorsally, 

 following along the anterior surface of the pelvic girdle, and passes to the inner 

 surface of the carapace. 



