THE FROG ii7 



serve that this large artery is a continuation of, and receives most 

 of the blood of, the left systemic arch. The dorsal aorta thus 

 receives most of its blood from the right arch. 



The coeliaco-mesenteric artery supplies the stomach and intestine 

 with blood. It soon divides into two branches,— the cceliac artery 

 and the anterior mesenteric,— the former supplying the stomach, 

 liver, and pancreas, and the latter the small intestine, rectum, and 

 spleen. 



Posteriorly to the cceliaco-mesenteric artery four to six pairs of 

 urogenital arteries spring from the ventral surface of the dorsal 

 aorta and go to the genital organs, kidneys, and fat bodies. Sev- 

 eral pairs of small lumbar arteries spring from the dorsal sur- 

 face of the aorta and supply the dorsal body wall. Near the hinder 

 end of the dorsal aorta the small median posterior mesenteric 

 artery leaves its ventral surface and runs to the rectum. 



The common iliac arteries, which are formed by the division of 

 the dorsal aorta, are large vessels which supply the hind legs. 

 A short distance from its origin each gives off two small arteries,— 

 the hypogastric, which supplies the rectum, bladder, and ventral 

 body wall, and the femoral, which goes to the thigh. After giving, 

 off these arteries the common iliac becomes the sciatic artery. 

 Follow it and its branches into the leg. 



Exercise 23. Draw a semidiagrammatic sketch showing these arteries 



so far as they have been observed. 

 Exercise 24. Draw a diagram of the entire arterial system. 



The Muscular System. In the land vertebrates most muscles 

 are attached at their two ends by means of tendons. One end is 

 usually attached to a more or less fixed and the other to a more 

 movable portion of the body, the former being called the origin of 

 the muscle and the latter its insertion. The middle part of the 

 muscle is called the belly ; by its contraction the origin and inser- 

 tion, and with them the skeletal pieces to which they are attached, 

 are brought nearer together. Muscles are usually attached to the 

 bones and cartilages ; thick fibrous membranes, called aponeuroses, 

 which often cover muscles and other organs, may, however, serve 

 the same purpose. 



