ALIMENTARY SYSTEM OF THE HADDOCK. 435 



Alimentary System. — Teeth are borne by the premaxillae, 

 the vomer, and the superior pharyngeal bones above, by the 

 dentaries and the inferior pharyngeal bone beneath. There 

 are no salivary glands, nor spiracles, nor posterior nares. A 

 small tongue is supported by a ventral part of the hyoid 

 arch. Five gill-clefts open from the pharynx ; their inner 

 margins are fringed by horny gill-rakers attached to the 

 branchial arches and serving as strainers. The gullet leads 

 into a curved stomach ; at the junction of stomach and 

 duodenum numerous tubular pyloric c»ca are given off; 

 into the duodenum opens the bile-duct from the gall-bladder 

 and liver ; the intestine passes gradually into the rectum, 

 which has an aperture apart from those of the genital and 

 urinary ducts. It will be noted that a pancreas is absent ; 

 perhaps the pyloric caeca take its place. Nor can one fail 

 to remark the darkly pigmented peritoneal membrane which 

 lines the abdominal cavity. 



Respiratory System. — Water that passes in by the mouth 

 may pass out by the gill-clefts ; the branchial chamber is 

 also washed by water which passes both in and out under 

 the operculum. The gill-filaments borne on the four 

 anterior branchial arches are long triangular processes, whose 

 free ends form a double row. As there are no partitions 

 between the five gill-clefts, the filaments project freely into 

 the cavity covered by the operculum. Along each arch and 

 filament there are blood-vessels, bringing the impure blood, 

 and removing it purified. On the internal surface of the 

 operculum lies a red patch, the pseudobranch or rudimentary 

 hyoidean gill. 



The swim-bladder lies along the dorsal wall of the abdo- 

 men ; the duct which originally connected it with the gut 

 has been closed. The dorsal wall of the bladder is so thin, 

 that the kidneys and vertebrae are seen through it; the 

 ventral wall is thick, and bears anteriorly a large vascular 

 rete mirabile, which receives blood from the mesenteric 

 artery and returns blood to the portal vein. 



Circulatory System. — The heart lies within a pericardial 

 chamber, separated by a firm partition from the abdominal 

 cavity. The blood from the body and liver enters the heart 

 by the sinus venosus, passes into the thin-walled auricle, and 

 thence to the muscular ventricle. From the ventricle it is 



