THE OPTIC NERVE 



883 



The Optic Chiasma (chiasma opticum), somewhat quadrilateral in form, rests 

 upon the tuberculum sellae and on the anterior part of the diaphragma sellae. 

 It is in relation, above, with the lamina terminalis; behind, with the tuber cinereum; 

 on either side, with the anterior perforated substance. Within the chiasma, the 

 optic nerves undergo a partial decussation. The fibers forming the medial part of 

 each tract and posterior part of the chiasma have no connection with the optic 

 nerves. They simply cross in the chiasma, and connect the medial geniculate 

 bodies of the two sides; they form the commissure of Gudden. The remaining and 

 principal part of the chiasma consists of two sets of fibers, crossed and uncrossed. 

 The crossed fibers which are the more numerous, occupy the central part of the 

 chiasma, and pass from the optic nerve of one side to the optic tract of the other, 

 decussating in the chiasma with similar fibers of the opposite optic nerve. The 

 uncrossed fibers occupy the lateral part of the chiasma, and pass from the nerve 

 of one side into the tract of the same side. 1 



Optic nerve 

 Crossed fibers 

 Uncrossed fibers 



Optic chiasma 



Optic tract 

 Commissure of Chidden 



Pulvinar 



Lateral geniculate body 

 Superior coUiculus 

 Medial geniculate body 



Nucleus of oculomotor nerve 

 Nucleus of trocMear nerve 

 Nucleus of abducent nerve 



Cortex of occipital lobes 

 FIG. 774. Scheme showing central connections of the optic nerves and optic tracts. 



The crossed fibers of the optic nerve tend to occupy the medial side of the nerve 

 and the uncrossed fibers the lateral side. In the optic tract, however, the fibers 

 are much more intermingled. 



1 A specimen of congenital absence of the optic chiasma is to be found in the Museum of the Westminister Hospital. 

 See also Henle, Nervenlehre, p 393, ed. 2. 





