150 Mr Twining on Single Vision, 



junt, nervos visorios nequaquam se intersecare, sed coire et 

 regredi ad eandem partem." 



Obs. 7. — Vesalius thus relates the dissection of the brain 

 and optic nerves of a woman, in L. iv. cap. 4, dc Corporis hu- 

 mani Fabrica: — " Mulier nobis obtegit, cui dexter quoque 

 oculusab ineunte aetate emarcuerat, sinistro interim integerrimo. 

 Mulieri dexter nervus toto progressu longe tenuior sinistro vise- 

 batur, non solum extra calvariae cavitatem, verum in exortu 

 quoque et in dextra congresses nervorum sede. Ac prseter- 

 quam quod dexter tenuis erat, durior quoque et rubicundior 

 cernebatur, uti sane et in adolescente : sed dexter non admo- 

 dum neque crassitie, neqne mollitie adhuc sinistro cedebat." 



After looking with particular attention to such instances of 

 diseased structure in the optic nerves and their thalami, as have 

 been observed connected with impaired functions, of the organs 

 of vision, we may reasonably attempt farther to elucidate the 

 subject under consideration, by referring to the most accurate 

 researches relating to the structure of the human brain and 

 optic nerves in a sound state. 



The labours of anatomists have not as yet detected any de- 

 cussation of fibres at the union of the optic nerves on the sella 

 turcica in the human subject. Vicq.-d'Azyr observed, that 

 when the human brain was hardened by immersion in alcohol, 

 and the union of the optic nerves examined, the medullary fi- 

 bres of the superior and inferior surfaces go direct to the eye 

 of the same side ; but the central part of this union of the op- 

 tic nerves contains a mixed mass, the direction of whose fibres 

 could not be ascertained. Wenzel observed the same structure 

 of the outer side of the optic nerves at that part, while a small- 

 er portion of the inner side of each nerve is inclined obliquely 

 towards the opposite side; but it was impossible to demon- 

 strate that any of the fibres crossed. — Vide Wenzel de peniti- 

 ori Structura Cerebri Hominis et Brutorum. This precisely 

 accords with the evidences from morbid anatomy, in observa- 

 tions 1st and 6th above stated. 



Reil and Haller, who dissected and studied the structure 

 of the brain with unremitting assiduity, have not been more 

 fortunate in their demonstrations than the other authors above 

 named. 



