496 



PISCES— FISHES. 



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 in to the liver (a) from the coeliac 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 from the caudal, 

 pelvic, and lumbar regions (the renal 

 portal system) ; blood leaves the kid- 

 neys 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 ccelom. 

 The blood contains, as usual, red 

 blood corpuscles and leucocytes. 



The dark red spleen lies in 

 the curve of the stomach. The 

 red thyroid gland lies just in 

 front of the anterior end of the 

 ventral aorta. The whitish thy- 

 mus gland is a paired structure 

 lying dorsally above the gills. 



Excretory and reproductive 

 systems. — The dark red kid- 

 neys lie far back on each 

 side of the vertebral column. 

 They are developed from the 

 hind part of the mesonephros. 

 Several tubes from each kidney combine to form a ureter. 

 The two ureters of the male open into the urogenital 

 sinus, whence the waste products pass out by the cloaca ; 

 in the female they open into little bladders, — the dilated 

 ends of the Wolffian ducts, — and thence by a common 

 aperture into the cloaca. 



Fig. 2ii. — Urogenital organs 

 of male skate. — From a speci- 

 men in Edinburgh Museum of 

 Science and Art. 



7\, Testis; Ep., epididymis; v.d., 

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

 seminal vesicle; s.s., sperm sac; 

 u.g.s., urogenital sinus ; Ct. t 

 cloaca. 



