6o4 



PHYLUM CHORDATA I CLASS PISCES — FISHES 



union they are reduced first to four and then to three efferent trunks, 

 which combine to form the dorsal aorta. 



From the efferent branchial of the hyoid arch a carotid arises, which 

 divides into internal and external branches supplying the brain and 

 head. The two internal carotids unite, and pass through a small hole 

 on the ventral surface of the skull. Just after the first and second main 

 efferent branches have united, a vertebral is given off, which passes 

 through a hole in the vertebral plate to the spinal cord and brain. 



The dorsal aorta gives off — (i) a 

 subclavian to each pectoral fin ; (2) a 

 coeliac to the stomach, duodenum, 

 and liver ; (3) a superior mesenteric 

 to the intestine, pancreas, and spleen ; 

 (4) spermatic arteries to the repro- 

 ductive organs ; (5) an inferior 

 mesenteric to the rectum ; (6) renal 

 arteries to the kidneys; (7) arteries 

 to the pelvic fins. It ends in the 

 caudal arterj^ 



At each end of the bow-shaped 

 sinus venosus there is a precaval 

 sinus. This receives venous blood as 

 follows : — (a) from the head by a 

 jugular vein ; {b) from the liver by 

 a hepatic sinus, which runs from one 

 precaval sinus to the other like the 

 string of the bow ; (c) from a large 

 posterior cardinal sinus (between the 

 reproductive organs) by a cardinal 

 vein on each side ; (d) from the 

 hind-fin by an epigastric, with which 

 brachials from the fore-limb unite 

 anteriorly. The great cardinal sinus 

 receives blood from the hind-limbs, 

 the kidneys, and other posterior 

 parts. 



Blood passes into the liver (a) from 

 the coehac artery, and {b) by portal 

 veins from the intestine (the hepatic 

 portal system) ; blood leaves the liver 

 by hepatic veins which enter the hepatic sinus. 



Blood passes into the kidneys (a) from the renal arteries, and (b) by 

 renal portal veins frcnn the caudal, pelvic, and lumbar regions (the 

 renal portal system) ; blood leaves the kidneys by posterior cardinal 

 veins, which enter the cardinal sinus. 



Into the precaval sinus there also opens the lymphatic trunk. 

 The heart lies in a pericardial cavity, which is connected with the 

 abdominal cavity by two fine canals, and is an anterior part of the 

 coelom. The blood contains, as usual, red blood corpuscles and 

 leucocytes. 



The dark red spleen lies in the curve of the stomach. The red 



s.s 



Fig. 3-1 1. — Urinogenital organs 

 of male skate. 



2\, Testis ; Ep., epididymis ; v.d., vas 

 deferens ; K., kidney ; v.s., seminal 

 vesicle ; s.s., sperm sac ; u.g.s., 

 urinogenital sinus; C/., cloaca. 



