(_b_) A cutaneous artery, which at first runs forwards to the base of the arm, and becomes spread out on the skin of the back of the head. [_In the Frog_ 1. _The carotid arch gives off_:-- (_a_) _A lingual artery supplying the tongue._ (_b_) _A carotid artery, running round the side of the œsophagus, and supplying the head. At its origin it is slightly swollen into the carotid gland._ 2. _The systemic arches run backwards on each side of the body, and meet posteriorly to form the dorsal aorta. Each systemic arch gives off_:-- (_a_) _A subclavian artery to the shoulder and fore-limb._ (_b_) _An occipito-vertebral artery to the head and the vertebral column._ (_c_) _An œsophageal artery to the dorsal wall of the œsophagus._ (_d_) _A laryngeal artery to the larynx._ _At the point where the dorsal aorta is formed, note the origin of the cœliaco-mesenteric artery which sends branches to the stomach, liver, intestine, and spleen._ _Trace the dorsal aorta backwards and note that it passes between the kidneys, to each of which it gives off four renal arteries and then it divides posteriorly into an iliac artery to each leg. The iliac artery is continued backwards as the femoral artery in the leg._ 3. _The pulmo-cutaneous arch gives off_:-- (_a_) _A pulmonary artery, running along the outer side of the whole length of the lung._ (_b_) _A cutaneous artery, which at first runs forwards and upwards, and then turns backwards, supplying the skin of the back and the sides of the head._] Make a complete sketch of the arterial system. [Illustration: FIG. 7.--Arterial System of Xenopus and Rana.] Cut out the heart, leaving attached to it as much as possible of the large vessels. Note the sinus venosus, truncus arteriosus, auricles, and ventricle. Open the auricles and observe the division between them and the openings of the veins passing into them. Make a section through the auricles and ventricle noting the thick muscular walls of the ventricle and the valves between it and the auricles. =Respiratory System and Alimentary System= (_continued_). 1. Remove the mylo-hyoid muscles to expose the hyoid apparatus. Pass a seeker through the glottis to one of the lungs and slit it open with a pair of scissors. Examine the structure of the lung. 2. Remove the whole of the alimentary canal with the lungs, liver, pancreas, and spleen, by cutting through the œsophagus and the large intestine before it joins the cloaca, and detaching it from the roof of the body cavity without injuring the kidneys and the reproductive organs. Draw the complete alimentary canal. [Illustration: FIG. 8.--Alimentary Canal of Xenopus and Rana.] Urinogenital System.