62 



AN INTRODUCTION TO ZOOLOGY 



C.G 



I.C. 



L.B 



it divides into a palatine branch, supplying the palate, part of the 

 oesophagus and the orbit, and a cerebral branch which passes through 

 a foramen in the base of the skull and spreads out over the brain. 



The Systemic Arch runs on laterally around the oesophagus to 

 unite partially with its fellow of the opposite side, and so give rise 



to the dorsal aorta, the main 

 arterial trunk of the posterior 

 part of the body. During its 

 passage around the oesophagus 

 the systemic arch on each side 

 gives off a number of branches. 

 The laryngeal and oesophageal are 

 two fairly small twigs, supplying 

 the larynx and the oesophagus 

 respectively. They are followed 

 by the occipito-vertebral artery, a 

 short trunk that divides into the 

 occipital, running forwards to the 

 back and sides of the head, and 

 the vertebral, which runs back 

 parallel with the vertebral column 

 and gives off branches to the 

 muscles of the back and to the 

 spinal cord. The sub-clavian is 

 the largest of the arteries coming 

 off from the arch. It runs straight 

 outwards, supplying the shoulder 

 girdle and the fore limb. 



The two arches run together on 

 the dorsal side of the body cavity 

 just below the vertebral column 

 about the level of the sixth verte- 

 bra, and the left communicates 

 with the right by a small opening, 

 but it is in the main continuous 

 with thecoeliaco-mesenteric artery, 

 the first great branch coming off 

 from the dorsal aorta. The cceliaco- 

 mesenteric quickly divides into two the cceliac and the mesenteric. 

 From the cceliac spring the gastric artery supplying the stomach and 

 pancreas, and the hepatic supplying the liver. The mesenteric, after 

 giving off the splenic to the spleen, splits into two main branches, 

 going to the remaining parts of the alimentary canal exclusive of the 

 end of the rectum. 



FIG. 20, Diagram of arterial 

 system. Rana. 



C., coeliac ; C.A., conus arteriosus ; C.G., 

 carotid gland ; C.M., coeliaco-mesenteric ; 

 Cu., cutaneous ; D.O., dorsal aorta ; E., epi- 

 gastric ; E.G., external carotid ; F., femoral ; 

 G., gastric ; Ge., genital ; H., Hepatic ; I., 

 iliac ; I.C., internal carotid ; L., laryngeal ; 

 L.B., ligamentum (ductus) botalli; L.S., left 

 systemic arch ; M., mesenteric and intes- 

 tinal ; O., occipital ; Oe., oesophageal ; O.V., 

 occipito-vertebral ; P., pulmonary ; P.M., 

 posterior mesenteric ; R.S., right systemic ; 

 R.V., recto-vesicular ; S., sciatic ; S.C., sub- 

 clavian ; Sp., spermatic ; T.A., truncus arte- 

 riosus ; V., vertebral. 



