SENSE OF SIGHT. 191 



(5) The Angular Gyrus is connected with the calcarine region by 

 association fibres. In it is seated the word-seeing and word- 

 understanding centre. It is developed round the posterior end of 

 the 1st temporal or parallel fissure (Fig. 176, p. 214). It is part 

 of the wall of the cerebral vesicle. The first temporal or parallel 

 fissure appears during the sixth month and is one of the primary 

 fissures. It is found in the brains of all primates except the 

 lowest. 



Summary. — It will thus be seen that three parts of the neural 

 tube are specialized in connection with sight. 



(1) The optic vesicle, an outgrowth from the fore-brain 

 (thalamencephalon). 



(2) The occipital end of the cerebral vesicle, which may also 

 be regarded as an outgrowth from the thalamencephalon. 



(3) The walls of the 3rd ventricle (thalamencephalon) and 

 mid-brain (mesencephalon), in which the basal optic ganglia are 

 developed. 



