86 DESCRIPTIONS OF PREPARATIONS. 



the course of the canals is therefore more easy to trace. There is much variety 

 in fish in the arrangement, &c., of these bodies. The canals are filled with a soft 

 mucus, secreted by goblet-cells in the lining epithelium. 



Other sense-organs terminal or end-buds occur on the general surface of 

 the body, on the fins, barbules when present, lips, as well as in the mouth, and 

 on the branchial arches. They generally project above the surface; the sensory 

 and supporting cells are of the same length, and both alike are terminated at their 

 free extremities by short fine points 



The brain fills the brain-case only in the young fish. The space developed 

 in the adult between the brain and the cranium is filled by a fatty arachnoid 

 tissue. There is some doubt how far the olfactory lobes do really correspond to 

 the structures called by the same name in higher animals. The apparently homo- 

 logous parts in Lepidosteus are parts of the cerebral hemispheres, and the true 

 olfactory lobes are very small. In some Teleostei, e. g. the Tench, the lobes are 

 as in many Elasmobranchii connected by a long peduncle to the brain. The 

 cerebral hemispheres are solid. They touch the optic lobes behind, and the 

 thalami optici are hidden from view. The pineal gland varies much in form, &c., 

 in fish. In the Perch its basal part is conical ; its middle region filamentous ; its 

 terminal part enlarged and fixed to the skull in the frontal region. The optic lobes 

 contain large ventricles. A peculiar fold -the fornix of Gottsche projects from 

 the region corresponding to the valve of Vieussens in Mammalia, and divides the 

 ventricles almost completely from the iter a 3 tio ad iv tum ventriculum. The cere- 

 bellum varies much in size and shape in Teleostei, bu it generally leaves the fourth 

 ventricle more or less uncovered. The sides of this ventricle are often enlarged at 

 the roots of the fifth nerve forming trigeminal lobes, = lobi posteriores, e. g. in the 

 Loach, Herring, and to a certain extent the Perch. Similar enlargements often 

 occur in relation with the roots of the vagus, forming vagal lobes, e. g. in Cyprinoids. 

 The pituitary body is composed of two parts, an anterior downward prolongation 

 of the infundibulum, and an appended saccus vasculosus. Close to this structure, 

 on either side, are the lobi inferiores or hypoaria, which are remarkably developed 

 in Teleostei, and contain ventricles communicating with the infundibulum. The 

 optic nerves, as in all Teleostei, cross or perforate one the other. The fifth and 

 seventh nerves are closely united at their roots. The glossopharyngeal quits the 

 skull by a special foramen as in Elasmobranchs, Ganoids, Dipnoi, and perenni- 

 branchiate Amphibia. The sense-organs of the mucous canals of the head are 

 supplied by the fifth nerve ; those of the lateral line by a branch of the vagus. 



The anterior narial aperture is very prominent in the Perch ; it is in some 

 fish prolonged into a tube. The posterior aperture rarely perforates the lip in 

 Teleostei, e. g. in some Muraenoids. The folds of the mucous membrane in the 

 Perch are, as is commonly the case, arranged in a rosette : in some instances they 

 are parallel to one another. In the eye, the cornea is flat, the lens spherical, the 

 retina non-vascular. There is a pecten or falciform process, highly vascular, and 

 pigmented, which projects into the vitreous humour, and terminates in a Campanula 

 Halleri, connected to the equator of the lens. The ear has the three typical semi- 

 circular canals. A sacculus and recessus cochleae are differentiated, and each 

 possess a crista acustica. The aquaeductus vestibuli is closed terminally, not open 

 as in Elasmobranchs on the surface of the head. There are generally two large 

 otoliths, a sagitta in the sacculus, an asteriscus in the recessus cochleae. 



