Part 5

(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.

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.

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.

Urinogenital System.

Note the kidneys, two elongated, flattened, dark-red bodies lying one on each side of the vertebral column towards the posterior end of the abdominal cavity. From the outer edge of each kidney a ureter arises and runs backward, opening into the cloaca on the dorsal side, opposite the opening of the urinary bladder.

In the male Platana note:--

(a) The testes, a pair of ovoid pale-yellow bodies attached to the dorsal wall of the body cavity by a fold of the peritoneum. They lie on the ventral sides of the kidneys and are connected to them by efferent vessels which pass into the kidneys.

(b) The corpora adiposa or fatty bodies lying in front of the kidneys.