88 DESCRIPTIONS OF PREPARATIONS. 



aortae. The conus arteriosus of the Elasmobranch and Ganoid has been absorbed 

 into the ventricle of the Teleostean. A slight trace of it is found in some Teleostei, 

 but in Bntirinus (Ctupeidae) alone are there two sets of valves. The persistent 

 valves appear to be those of the distal row of the Ganoid and Elasmobranch. The 

 ventral aorta gives off (i) the fourth and third branchial arteries, which have a 

 common origin, and (2) the second and first arteries separately. The veins unite 

 dorsally on each side into an epibranchial artery, and in the same manner as the 

 arteries rise from the ventral aorta. Each epibranchial gives off the common carotid 

 anteriorly, and the two carotids unite by a cross vessel which passes above the 

 parasphenoid. Posteriorly, the two epibranchials fuse to form the subvertebral aorta. 

 By these unions a circulus cephalicus is formed from which the external and internal 

 carotids' arise anteriorly, and into which the hyoidean artery falls dorsally. This 

 artery rises from the ventral end of the first branchial vein, and in its course it sup- 

 plies the pseudobranchia. In the Perch a caeliaco-mesenteric artery, which supplies 

 most of the abdominal viscera, springs from the right epibranchial before it fuses 

 with its fellow. The blood from the abdominal viscera (stomach, pyloric append- 

 ages, spleen, intestine, air-bladder in part) flows into a hepatic portal system. The 

 genital (spermatic or ovarian) vein enters the left ductus Cuvieri. The caudal vein 

 when it enters the abdomen divides into a right and left branch. The former 

 anastomoses with the right cardinal vein, and the latter, which is small, is also con- 

 nected to the right cardinal. There is a renal-portal circulation. The left cardinal 

 vein rises from the anterior part of the left kidney and is not directly connected 

 to a branch of the caudal vein. Both cardinal veins unite anteriorly, each with 

 the corresponding jugular vein, forming the right and left superior cavae or ducts 

 of Cuvier. A vein the inferior jugular lies dorsally to the heart. It is best 

 developed on the left side, collects blood chiefly from the inferior part of the head, 

 and falls into the left duct of Cuvier. 



The thyroid gland is broken up into lobules, and lies ventrally to the ventral 

 aorta, but some of its lobules are found distributed for a short distance along the 

 roots of the branchial veins. They are red in colour. The thymus is paired, 

 and each part lies behind and dorsally to the branchial arches, internally to the 

 supra-clavicle so-called. The kidneys are placed on either side of the vertebral 

 centra. They enlarge anteriorly and coalesce, and are perforated by the cardinal 

 veins. This region of the kidneys in many Teleostei was found by Professor Balfour 

 to consist of a vascular lymphatic tissue, and it does not, as is generally stated, 

 appear to be a persistent head-kidney or pronephros. In the Perch the kidneys 

 thin out posteriorly ; in the Pike they thicken and extend beyond the abdominal 

 cavity into the caudal region. There are two ureters which rise from the ventral 

 surface of the glands. They are fine tubes which pass ventrally downward behind 

 the posterior end of the air-bladder, unite, and at the place of union develope a 

 large simple urinary bladder. This structure, the form of which varies much in 

 fish, does not correspond with the urinary bladder of higher animals, which is 

 derived in development from the anterior (ventral) wall of the intestine, and 

 either represents (Amphibia) or is a remnant (Sauropsida, Mammalia) of the 

 allantois. 



The testes are paired ; they are rarely single in Teleostei. The inactive organ 

 is semi-transparent ; the active organ varies much in size, shape, and lobulation, 



