An American text-book of physiology . nnected with the retina, but others added from the superposed parts of thebrain. In the higher mammals it was shown by von Gudden ^ tiiat in the chiasmathe majority of tlje fibres forming one optic nerve pass to the tract of theopposite side, but that a portion of the fibres remain in the tract of the sameside. This was inferred because removal of one optic bulb caused in youngrabbits a degeneration in the associated optic nerve and also in both optictracts—most marked, however, in the tract of the side opposite to the lesion. ^ Onufrowicz: Exper. Beitrag
An American text-book of physiology . nnected with the retina, but others added from the superposed parts of thebrain. In the higher mammals it was shown by von Gudden ^ tiiat in the chiasmathe majority of tlje fibres forming one optic nerve pass to the tract of theopposite side, but that a portion of the fibres remain in the tract of the sameside. This was inferred because removal of one optic bulb caused in youngrabbits a degeneration in the associated optic nerve and also in both optictracts—most marked, however, in the tract of the side opposite to the lesion. ^ Onufrowicz: Exper. Beitrag zur Kenntniss des centralen Urspriinges des Nervus acus-ticus, Inaug. Diss., 1885. ^ von Gudden : Gesammelle und hinterlassene Abhandlangen, Wiesbaden, 1889. 680 AN AMERirAA TEXT-HOOK OF PIIYSIOhOQY. Conversely, the section of one optic tract causes a degeneration in both opticnerves, the nerve of tlio side opposite to the lesion being most affected, and asmaller degeneration a])pearing in the nerve of the same side (see Fig. 181).. Pig. 181—Illustrating the relations of the afferent fibres in the optic nerve. The crossed fibres areindicated by solid lines, the uncrossed fibres by broken lines : A, nasal side of the right eye; T, temporalside of the same ; G. E, geniculutum externum : P, pulvinar; C Q, quadrigeminum antcrius. It appears from this that in the higher mammals an optic tract is composedof fibres from both optic nerves, but mainly of fibres from the nerve of theopposite side. In the fish, amphibia, reptiles, and birds—except the owls—as well as in the lower mammals (mouse and guinea-pig, for example) thedecussation appears to be complete.^ For the partial decussation in the owlsthe evidence is physiological. This distribution of the optic fibres was asso- Ferrier: The. Croonian Lectures on Cerebral Localization, London, 1890, p. 70. Singer und Miinzer: Denkschriflen der Classe der kais. Akademie der Wissen-achaften, 1888, Ed. Iv. CENTRAL NER
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