1 86 PHYLUM CHORD ATA 



Exercise 18. Draw a semidiagrammatic sketch showing the distribu- 

 tion of these arteries so far as observed. 



The middle arch, the systemic, suppUes the greater part of the 

 body with blood. The two sides of the arch pass dorsally, one 

 on each side, around the oesophagus to the dorsal side of the 

 body cavity, where they meet and form the dorsal aorta. This 

 vessel runs just beneath the spinal column to the hinder part of 

 the body cavity, where it divides into two arteries, the iliacs, 

 which go to the hind legs. 



Lift up the stomach and find the dorsal aorta ; follow it for- 

 ward to the meeting point of the two sides of the systemic arch, 

 and then follow each side of the .arch to the heart. Each side of 

 the arch gives off the subclavian, occipito vertebral, oesophageal, 

 and laryngeal arteries. 



These arteries leave the arch near together. The subclavian 

 is the largest and supplies the shoulder and foreleg. Follow it 

 and its branches. The oesophageal and occipitovertebral are 

 close together and go to the head, a branch of the latter — the 

 vertebral — also passing back along the dorsal surface of the 

 spinal column. The laryngeal arises in front of the others and 

 goes to the head. 



Just behind the point of union of the two sides of the systemic 

 arch the dorsal aorta gives off the cceliacomesenteric artery. 

 Observe 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 coeliacomesenteric artery supplies the stomach and intes- 

 tine with blood. It soon divides into two branches, the coeliac 

 artery and the anterior mesenteric, the former supplying the 

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

 rectum, and spleen. 



Posteriorly to the coeliacomesenteric artery four to six pairs 

 of urinogenital arteries spring from the ventral surface of the dor- 

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

 Several pairs of small lumbar arteries also spring from the dorsal 

 surface of the aorta and supply the dorsal body wall Near the 



