GENERAL SURVEY OF THE FROG 9 



1. Circulatory system. This consists of the heart, the arteries (vessels leaving 

 the heart), the veins (vessels entering the heart), and the capillaries (microscopic 

 vessels between the ends of the arteries and the beginnings of the veins) . Remove 

 the pericardium by cutting it off with a fine scissors, and examine the heart. 

 The chambers of the heart are called ventricle, auricles, sinus venosus, and conus 

 arteriosus. The ventricle is the posterior, thick-walled, conical portion, the 

 point of the cone being designated as the apex of the ventricle, and the base of 

 the cone, the base. The auricles are the two dark-colored, thin-walled sacs 

 anterior to the ventricle. Extending from the right side of the base of the 

 ventricle obliquely forward between the auricles is a tube, the conus arteriosus, 

 which forks into two trunks leading away from the heart (Holmes and most other 

 textbooks erroneously refer to this chamber of the heart as the bulbus arteriosus). 

 To locate the sinus venosus, turn the heart up so that the apex points anteriorly, 

 and, putting the heart on a stretch, identify a small chamber appearing as a 

 dorsal and posterior continuation of the auricles, from which, however, it is 

 separated by a distinct white line. Three veins, dark red tubes, will be seen 

 emerging from the liver to enter the sinus venosus at its posterior border, and 

 each of its sides receives a vein which runs along the margin of the adjacent 

 auricle. Through these large veins all of the venous blood in the body is returned 

 to the sinus venosus which passes it on into the right auricle. Note the mem- 

 brane by which the pericardial sac is attached to the serosa of the liver; this is 

 the coronary ligament of the liver. 



2. Respiratory system. This system consists of the glottis, noted in the 

 study of the floor of the mouth, a pair of lungs, and the larynx, a chamber con- 

 necting the lungs with the glottis. The lungs will be found attached to the 

 anterior wall of the coelome, lateral to the heart. Push the liver and other 

 structures aside in order to see them. Each is closely invested by a sac of 

 peritoneum. The larynx will be studied later. 



3. Digestive system. Its parts are the esophagus, stomach, small intestine, 

 large intestine, and digestive glands. The esophagus lies dorsal to the heart and 

 will be seen more clearly at a later time. It passes into the elongated cylindrical 

 stomach, a conspicuous white organ on the left side of the body dorsal to the 

 liver. (If the animal is a female, the large ovaries, voluminous lobed black and 

 white masses, will obscure the rest of the abdominal viscera, and may be removed, 

 at least on the left side.) From the end of the stomach, trace the small intestine, 

 a coiled tube, to its enlargement into the large intestine. Locate the urinary 

 bladder, a thin- walled, usually shriveled sac at the extreme posterior end of the 

 coelome. The large intestine passes through the bony ring formed by the pelvic 

 girdle, and opens to the exterior through the anus. The entire tube from mouth 

 to anus is the alimentary canal. Associated with the alimentary canal are two 

 digestive glands, the liver, already noted, and the pancreas. The latter is a 



