1424 A MANUAL OF ANATOMY 



Development. — ^I'he corpora mammillaria are developed from the ventral 

 aspect of the thalamencephalon or diencephalon. Up to the fourth month 

 of intrauterine life they are represented by a single corpus mammillare, but 

 after that period this divides into two corpora. 



The tuber cinereum is an elevated area of grey matter which Ues 

 in front of the corpora mammillaria and behind the optic commissure, 

 the anterior portion of each optic tract being on either side. It is 

 continuous anteriorly with the lamina terminalis, and on either side 

 with the grey matter of the locus perforatus anticus. 



In the outer part of the tuber cinereum, in the vicinity of the optic tract, 

 there is a collection of nerve-cells, which is variously spoken of as the basal 

 ganglion of Meynert or the supra-optic nucleus of Cajal, and which is con- 

 nected with the fibres of the commissure of Giidden. 



Behind the tuber cinereum, and in front of the corpora mammillaria, there is 

 a small prominence, mesially placed, called the eminentia saccularis of Retzius, 

 who regards it as the homologue of the saccus vasculosus of some lower verte- 

 brates, e.g., fishes. 



Along the outer side of the tuber cinereum, close to the innermost 

 fibres of the optic tract, there is a strand of grey matter containing 

 nerve-ceUs. This collection of cells is known as the basal optic 

 ganglion, or supra-optic nucleus. 



The infundibulum is a funnel-shaped stalk which extends down- 

 wards from the anterior part of the inferior surface of the tuber 

 cinereum to the posterior lobe of the pituitary body. Its upper 

 part is hollow, and contains the infundibular recess or diverticulum 

 of the cavity of the third ventricle. The infundibulum is the 

 peduncle of the posterior lobe of the pituitary body. 



Lamina Terminalis. — This is a thin plate of grey matter which 

 extends between the upper surface of the optic commissure and the 

 rostrum of the corpus callosum near the genu. On either side it is 

 connected with the grey matter of the locus perforatus anticus. It 

 forms the lower part of the anterior wall of the third ventricle. 



Development. — The lamina terminalis represents the terminal part of the 

 ventral wall of the embryonic neural tube, and it originally connects the 

 anterior wall of the telencephalon with that of its fellow. 



For the pituitary body and infundibulum, see Index. 



Optic Nerve, Optic Commissure, Optic Tract, and Optic Radiation. 



The optic nerves, or nerves of sight, in the cranial cavity are 

 connected together at the optic commissure, where some of the fibres 

 decussate. From the back part of the commissure each nerve, under 

 the name of the optic tract, passes backwards round the crus cerebri 

 to its cerebral connections. 



The optic commissure or chiasma is somewhat quadrilateral, 

 and rests upon the olivary eminence and optic groove of the 

 sphenoid bone. It lies in front of the tuber cinereum and infundi- 

 bulum, and its superior surface is connected with the lamina 

 cinerea, and is intimately related to the anterior part of the floor 



