208 THE FROG— THE PLATANA 



runs straight across to meet its fellow in the middle line to form the abdominal vein. 

 At the origin of the abdominal vein a small rectal vein is given off to the rectum. 

 In order to expose the pelvic vein clearly, cut through the pelvic girdle on one side 

 and carefully sever the muscles of the leg from the vicinity of the pelvic girdle.] 



C. Arterial System (part). 



Distend the oesophagus with cotton-wool or a roll of paper in order to 

 show the blood-vessels clearly, and follow out the anterior part of the arterial 

 system. The two branches of the short ventral aorta or " truncus " at once 

 divide into the following three arterial arches : — 



(a) The carotid arch, which gives off the arteries to the head region. 



(b) The systemic arch, which curves round the oesophagus. 



(c) The pulmo- cutaneous arch to the lungs and the skin. 



Fourth Day 

 Arterial System (continued). 



1. Trace the carotid arch, which gives off : — 



(a) A lingua] artery supplying the tongue. 



(b) A carotid artery suppljdng the head. It goes round the side of the 



oesophagus. A slight swelling at its origin is the carotid gland. 



2. Trace the systemic arches which curve round the oesophagus, one on each 

 side, towards the dorsal surface of the body. Going backwards and inwards, 

 the two systemics gi'adually. converge to meet in front of the kidneys, and there 

 unite to form the dorsal aorta. Each systemic arch gives off : — 



(a) A laryngeal artery to the larynx. 



(b) An oesophageal artery to the dorsal wall of the oesophagus. 



(c) An occipito-vertebral artery to the side of the head and the vertebral 



column. 



(d) A subclavian artery to the shoulder and fore-limb. 



At the point where the dorsal aorta is formed, note the large coeliaco- 

 mesenteric artery which arises there, and which sends branches to the stomach, 

 liver, intestine, and spleen. 



Trace the dorsal aorta backwards, and note that it passes between the 

 kidneys, there gives off four or six renal arteries, and then divides posteriorly 

 into two iliac arteries which supply the legs. The iliac artery is continued 

 backwards as the sciatic artery in each leg, and divides above the knee into the 

 peroneal and the tibial artery to leg and foot respectively. 



3. Trace the pulmo-cutaneous arch, which gives off : — 



(a) A pulmonary artery along the outer side of the whole length of the lung. 



(b) A cutaneous artery, which passes forward close behind the ear, and then 



turns sharply backwards to supply the skin of the back and the sides 

 of the head. 



