NERVES. SENSE ORGANS. 195 



e.g. in Orthagoriscus mola it is barely as long as the brain and 

 hardly reaches beyond the skull. In such cases it ends in a 

 sJender hlum terminale. 



The central canal usually contains a fibre * (Reissner's fibre), which 

 extends trom the anterior end of the optic lobes, with which it is continuous, 

 backwards along the whole length of the central canal. It consists of a 

 biuidle ot nerve tibres, and communicates with the tissues of the spinal 

 cord throughout its course. It appears to be absent in blind fishes. 



In some Teleosteans (Ctenolabrus, Pleuronectes, etc.) giant nerve cells f 

 are tound in the posterior fissure of the spinal cord, their neurites passing 

 into the substance of the cord. 



The cranial nerves t resemble in their general arrangement 

 those of other fishes. 



The ramua ophthalmicus profundus if present is 

 much reduced. Tiiere is a dorsal branch of the fifth 

 nerve — the ramuts lateralis accessorius or r. recurrens 

 irigemini — which receiving branches from the facial 

 and vagus passes dorsalwards in the cranium to 

 perforate the frontal bone. It then travels backwards 

 near the skin to supply the skin of the trunk near the 

 dorsal fin (sense-buds and pit-organs). It appears 

 to be composed partly of so-called communis (afferent- 

 visceral) fibres (ramus lateralis accessorius), and partly FigT 115. — Horl- 

 of lateralis fibres supplying pit-organs and derived from ^^^^ v. th^^*'°° 



the facial. of Esox lurius 



(from Claus). Co 

 cornea ; L Ions ; 



Sense organs. The olfactory organ is Pf rroressus fai- 



*= .7 6 ciformis ; CH 



usually provided with two OpenmgS. campanula Hal- 



mi 1- 111! . •e''' : -^'^ °P*'<= 



The eye is distinguished by the possession nerve; sc ossifl- 



n 1 1 . 1 • 1 cations in the 



of a flat cornea and a sclerotic which is sclerotic. 

 frequently more or less ossified. The lens 

 is closely approximated to the cornea, the anterior chamber 

 of the eye being small. Traversing the vitreous humour, some- 

 what on the lower side of the eyeball, and extending from the 

 entrance of the optic nerve to the eye, is a band of tissue (a 

 process of the choroid coat) containing blood vessels and smooth 

 muscular fibres ; this is the processus falciformis. At its point 

 of attachment to the lens it is swollen into the so-called cam- 

 panula halleri. One of the functions of this structure is said to 

 be that it assists in accommodation for vision of distant objects, 



• Sargant, Anat. Anzeiger, 17, 1900, p. 33. A similar fibre has been 

 described in Petromyzon. 



t Sargant, Anat. Anzeiger, 15, 189S, p. 212. 



j Stannius, op. cit. Cole, Gadus, Trans. Lin. Soc, (2), 7. Herrick, 

 Menidia, Journ. Comp. Neurol., 9, 1899. 



