. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. ~\ a a, chiasma ; b, optic nerve divested of neurilema and exhibiting lamina1 on one surface ; c. sclerotic coat. Desmoulins, who has paid the greatest at- tention to these varieties, inferred as the result of his extensive researches, that the plaited arrangement of the optic nerve in fish, and its laminated condition in birds bears pro- portion to the perfection of vision in the ani- mals under consideration; for those birds which are endowed with the most powerful piercing sight possess the laminated structure at a ma
. The cyclopædia of anatomy and physiology. Anatomy; Physiology; Zoology. ~\ a a, chiasma ; b, optic nerve divested of neurilema and exhibiting lamina1 on one surface ; c. sclerotic coat. Desmoulins, who has paid the greatest at- tention to these varieties, inferred as the result of his extensive researches, that the plaited arrangement of the optic nerve in fish, and its laminated condition in birds bears pro- portion to the perfection of vision in the ani- mals under consideration; for those birds which are endowed with the most powerful piercing sight possess the laminated structure at a maximum of developement. For example, birds of prey, such as the eagle, the falcon, and the kite, evince an acuteness of this faculty truly surprising; from heights in the atmos- phere, at which they are themselves almost invisible, they discover their prey on the ground and pounce on it with the most unerring cer- tainty, whilst at the trifling distance of a few yards other animals recognise such objects with difficulty: now birds of this class afford the most perfect specimens of the laminated optic nerve. It is further stated on the same autho- rity that birds which at short distances possess remarkably quick and accurate powers of vision (more especially when in such cases this faculty is exercised in media of different degrees of density) are also provided with laminated optic nerves, and that most fish in which the plaited optic nerves occur are of pre- dacious habits, and consequently require posv- erful organs of vision just as the birds of like propensities. The writer has examined the optic nerves in the stork, kingfisher, eagle, &c., and in them, as well as in all the fishes which have fallen within his reach, his dissections have amply verified the anatomical descriptions given by Desmoulins. It is difficult to explain the superior sensi- bility supposed to be thus conferred on the. Please note that these images are extracted from scanned page images that may hav
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