430 THE ANIMAL KINGDOM. 



developed. The ciliary muscle is perhaps wanting. The lens is spheroidal, 

 and almost touches the cornea. A falciform process is present in most 

 Teleostei ; it ends in a bulbus expansion, the Campanula Halleri, which is 

 attached at the equator of the lens. It is pigmented, vascular, and supplied 

 with nerves ; the Campanula contains muscular tissue, and is probably 

 concerned in accommodation. A choroid gland or bipolar vascular rete 

 is found in most Teleostei close to the optic nerve, and lying between the 

 argentea and the choroid coat. It receives the blood of the ophthalmic 

 artery coming from the pseudobranchia, and is supposed to represent the 

 spiracular gill. The auditory structures are completely inclosed in cartilage 

 in Elasmobranchii and Dipnoi, but in Holocephali, Ganoidei, and Teleostei 

 the inner, i. e. cranial, wall is membranous. The aquaeductus vestibuli 

 opens externally on the head in most Elasmobranchii. The connection 

 between the vestibule and saccule is closed in Batoidei, bony Ganoidei, and 

 some Teleostei ; and in the latter the cochlear outgrowth (= lagena) is 

 large. It contains a small otolith, the asteriscus, whilst the saccule has one 

 of great size, the sagitta. Among Teleostei in some Acanthopteri (Percoids 

 and Sparoids) a process of the air-bladder is applied to a membranous 

 fenestra in the auditory capsule ; in the Clupeidae a similar process enters 

 the capsule and comes into relation with the vestibule, whilst in Siluroidei 

 and Cyprinoidei a chain of bones derived from the vertebral centra and 

 ribs connects the air-bladder to the vestibule. 



Fish are very rarely edentulous, e. g. Acipenser, some Lophobranchii, 

 but the former has larval teeth afterwards lost. Protopterus among Dipnoi, 

 has two conical, Ceratodus two elongate vomerine teeth, whilst the palato- 

 pterygoid bone and the splenial bear peculiar ridged plates. The palato- 

 pterygoid cartilage and the mandible are dentigerous in Elasmobranchii 

 and Holocephali. In bony Ganoidei and Teleostei the praemaxillae, vomers, 

 parasphenoid, dentary, and branchial arches must be added to the list. 

 The maxilla carries teeth in bony Ganoidei, but only in a few Teleostei, e.g. 

 Salmonidae. The teeth are composed of dentine, which may obliterate 

 the pulp cavity, and is coated or tipped with structureless enamel. The 

 dentine in Lepidosteus is folded, as in many Stegocephali (Amphibia) ; and 

 the plates of Myliobatis (Batoidei) are composed of hexagonal denticles set 

 side by side, as in Orycteropus among Edentate Mammalia. The form of 

 the teeth varies much : serrated or pointed plates in many Sharks : flat 

 plates in Cestracion and some Rays (Myliobatis} ; very various but usually 

 conical in Ganoidei and Teleostei. They are attached or implanted in a 

 fibrous membrane, which moves forwards over the edge of the jaw in 

 Elasmobranchii ; by an elastic ligament which allows the tooth to bend 

 backwards in some Gadidae, Lophius, the vomerine and palatal teeth of 

 Esox, among Teleostei ; in sockets, e.g. in Sphyraena (Barracuda Pike), and a 

 few other Teleostei, to which they may be anchylosed, as in Lepidosteus ; 



