text:  [30] This reasoning of Dr Brown's is founded upon an assumed analogy between the structure of the optic nerve and the structure of the olfactory nerves and other sensitive nerves and is completely disproved by the physiological observations of Treviranus who has shown that no such analogy exists: that the ends of the nervous fibres in the retina being elevated into distinct separate _papillae_ enable us to perceive the extension and discriminate the position of visible bodies while the nerves of the other senses being less delicately defined are not fitted to furnish us with any such perception or to aid us in making any such discrimination