500 FISHES. 



The fin rays of each pelvic fin are attached to a thin 

 innominate bone, which may be a basal element of the fin, 

 or the rudiment of a pelvic girdle. 



Nervous System. 



The relatively small cerebral hemispheres, the thalamen- 

 cephalon with its inferior lobes and infimdibulum, the large 

 optic lobes, the tongue-shaped cerebellum which conceals 

 most of the medulla oblongata, have their usual general 

 relations. Each of the olfactory nerves is at first double ; 

 their bulb-like terminations lie far from the brain behind 

 the nasal sacs. The large optic nerves cross one another 

 without fusion at a slight distance from their origin, other- 

 wise the nerves generally resemble those of the skate. 



In the large eyes, the different parts will be readily identi- 

 fied; the small nasal sacs with plaited walls have double 

 anterior apertures ; the vestibule of the ear contains a large 

 otolith, and another very small one in a posterior chamber. 

 The dark lateral line, covered over by modified scales, lodges 

 sensory tubes, and is innervated by a branch of the vagus. 



Alimentary System. 



Teeth are borne by the premaxillse, 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 caeca 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. A 

 pancreas is absent ; perhaps the pyloric caeca take its 

 place. The peritoneal membrane which lines the abdominal 

 cavity is darkly pigmented. 



Respiratory System. 



Water that passes in by the mouth may pass out by the 

 gill clefts ; the branchial chamber is also washed by water 



