910 



THE NER VE SYSTEM 



optic chiasm; caudad thereof is the infundibular recess in the tuber. The epi- 

 physeal recess is seen between the habenular commissure and the posterior com- 

 missure. Dorsad of the pineal body is a diverticular recess of variable extent 

 (recessus suprapinealis). 



If the segmentation of the fore-brain into two divisions be adopted ultimately, 

 it will be necessary to allot one portion of the third ventricle (between the thalami) 

 to the diencephalon (hence diacele), and the rest to the telencephalon (the medial 

 cavity of which is termed the aula by Wilder). 



In anticipation of the description of the cerebral hemispheres we may consider 

 here the remaining structures in the floor of the third ventricle, usually included 

 under the head of the pars optica hypothalami of the telencephalon, in order to lead 

 up to a description of the cerebral connections of the optic tract. 



External Morphology of the Optic Portion of the Hypothalmus. This 

 includes the tuber cinereum and pituitary body or hypophysis, the lamina terminalis, 

 the optic chiasm , and the optic tracts. 



LAMINA 

 TERMINALIS 



ANTERIOR 

 COMMISSURE 



OPTIC 



COMMISSURE 



INFUNDIBULUM 



CRUS CEREBRI 



CORPUS ALBICANS 



POSTERIOR CEREBRAL 

 ARTERY 



/f!?. 



FIG. 667. The pituitary body, or hypophysis, in position. Shown in median sagittal section 



(Testut.) 



The tuber cinereum (Fig. 664) is a thin-walled conical projection in the inter- 

 crural space cephalad of the corpora albicantia. Its apical portion is attenuated 

 to form the stalk of the pituitary body; this is generally termed the infundibulum, 

 while the cavity of the funnel-shaped diverticulum is called the infundibular 

 recess of the third ventricle. The gray lamina composing the tuber is continuous 

 with the central ventricular gray, and therefore with the lamina terminalis. 



The pituitary body or hypophysis is a structure of twofold origin, giving rise 

 to a division into a prehypophysis and a posthypophysis. The posthypophysis 

 alone is of neural origin, developing as a ventral diverticulum from the* primitive 

 neural tube. The prehypophysis or epithelial lobe, develops from the stomodeum, 

 b or buccal cavity, as a tubular diverticulum (Rathke's), which eventually loses its 

 connection 1 with the oral tissues to become included within the cranial cavity 

 and intimately attached to the neural bud. Both pre- and posthypophysis are 

 therefore of ectodermal origin and have developed from a conjunction of "surface 

 tissues which have migrated from opposed (ventral and dorsal) parts through the 

 head! The prehypophysis is much the larger and somewhat embraces the post- 

 hypophysis; the two are inseparable, however, and together occupy the fossa 

 hypophyseos of the sphenoid. 



i Occasionally the channel persists as the craniopharyngeal canal. 



