THE SPECIAL ANATOMY OF THE FROG 45 



anterior parts of the head, and one behind the eye for the upper and lower jaws. 

 Remove all muscles from the vertebral column, and note the intricate branches 

 of the vertebral artery to the vertebrae. 



The two systemic arches from the two sides of the body now converge and 

 unite to form a single large vessel, the dorsal aorta. The dorsal aorta lies in the 

 cisterna magna, above the kidneys, and the pleuroperitoneum must be broken 

 through in the usual way to one side of one of the kidneys in order to follow this 

 vessel. At the point of union of the systemic arches, the large coeliaco-mesenteric 

 artery arises. Trace the branches of this artery. It divides into a coeliac, 

 which supplies the stomach, pancreas, and liver (right and left gastric arteries, 

 and hepatic artery), and an anterior mesenteric, which gives off a short branch 

 to the spleen (lienal artery), a number of branches to the small intestine (intes- 

 tinal arteries), and one or more branches to the large intestine (anterior haemor- 

 rhoidal arteries). 



Posterior to the origin of the coeliaco-mesenteric, the dorsal aorta gives rise 

 to a number of small paired urino genital arteries, which supply mainly the kid- 

 neys, but branch also to the fat bodies, and reproductive organs and their ducts. 

 In the same region, one to four pairs of small lumbar arteries arise from the aorta 

 and pass to the dorsal body wall. 



The dorsal aorta next gives off a single median branch, the posterior mesenteric, 

 to the large intestine, and shortly after this bifurcates into two large arteries, the 

 common iliac arteries. Each common iliac soon gives rise to two branches. One 

 of these, the epigastrico-Desical artery, branches almost immediately into an 

 epigastric artery for the muscles of the lateral and ventral abdominal walls, and 

 a recto-vesical artery for the urinary bladder and the rectum. The other is a 

 small artery to the urinogenital ducts. The iliac then supplies a small femoral 

 artery for the muscles of the thigh and continues down the leg as a large vessel, 

 the sciatic artery. 



Make an outline of the frog and its organs and put in the arteries, showing 

 their proper location and distribution. All of the arteries mentioned can be 

 readily found in well-injected specimens. Omit those that you could not identify. 



Be able to trace the blood from any part to any other part. 



F. THE CIRCULATORY SYSTEM: THE STRUCTURE OF THE HEART 



The four parts of the heart, the sinus venosus, the auricles, the ventricle, and 

 the conus arteriosus, have already been noted. Draw the heart from the side; 

 show these parts. 



The dissection of the heart should not be attempted except upon a well- 

 preserved, uninjured heart. The heart of injected specimens cannot be used 

 (Holmes, pp. 64-68). With a fine scissors remove the ventral wall of the ven- 

 tricle, the ventral wall of each auricle, and the ventral wall of the conus arteriosus 



