. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 770 OPTIC NERVES. part of their course. The conclusions arrived at by such modes of investigation were un- satisfactory, and remarkable for much dis- crepancy. 1. Some maintained that the nerves are merely placed in exceedingly close juxta- position in the chiasma, without any inter- crossing of their respective filaments, and that each tractus opticus in reality passes on to form the optic nerve of its own side. These views were supported by Vesalius,* who detailed the particulars of a case in which after death the two
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. 770 OPTIC NERVES. part of their course. The conclusions arrived at by such modes of investigation were un- satisfactory, and remarkable for much dis- crepancy. 1. Some maintained that the nerves are merely placed in exceedingly close juxta- position in the chiasma, without any inter- crossing of their respective filaments, and that each tractus opticus in reality passes on to form the optic nerve of its own side. These views were supported by Vesalius,* who detailed the particulars of a case in which after death the two optic nerves were found perfectly distinct from each other throughout their whole course, and consequently no chiasma existed, although, during life, vision had been unimpaired; and the same hypothesis was strengthened by Santorini and others, who, in certain instances where one eye had been destroyed many years before death, observed on the post mortem examination the correspond- ing optic nerve atrophied as far back as the chiasma, and the tractus opticus of the same side wasted, while the nerve and tractus of the opposite side were perfectly healthy. 2. Others were persuaded that a perfect de- cussation exists in the chiasma, and that all the filaments of the tractus opticus of one side pass fairly across to form the optic nerve of the oilier, and vice versa. In favour of this opinion it was urged that in the majority of cases of long- continued blindness of a single eye the opposite tractus opticus, and not the tractus on the same side with the affected eye, becomes atrophied. Scemmerring observed several such cases in the human subject, and traced the same appearances in the horse, dog, squirrel, rabbit, hog, cat, and chamois : and Cuvier preserved in spirits the brain of a horse in which the wasting of one optic nerve continued backwards into the oppo- site tractus. The evident manner in which the optic nerves in osseous fish cross each other (see fig. 407) was also cons
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