THE BEAIN AND SPINAL COKD. 



205 



The Lamina Cinerea or lamina terminalis (Fig. 167) represents 

 the anterior end of the neural tube. In the adult it stretches 

 between the optic chiasma, which is developed on the floor of the 

 3rd ventricle and the rostrum of the corpus callosum. Its 

 development will be described later, but it retains with little 

 alteration its early simple structure. The inter-peduncular space, 

 which forms the floor of the 3rd ventricle, also retains in the 

 adult to a considerable extent the simple embryonic form. In it 

 are developed the corpora albicantia and posterior perforated 

 space. 



The Optic Thalami are formed in the lateral walls of the fore- 

 brain (thalamencephalon) and in the adult occupy the whole 

 extent of this wall. At first they are completely exposed on 

 the outer aspect of the brain (see Fig. 154), but after the cerebral 

 vesicles grow out from the antero-lateral angles of the fore-brain 

 (3rd ventricle) they are prolonged backwards and downwards over 

 the optic thalami and thus bury them (Figs. 173, 174, and 175). 

 As may be seen from Fig. 169, the optic thalami, with the internal 



long, fis.-, , corp. callosum 



Island of 

 Reil. 



claustrum 



deso. horn 



uelum interposition 



caudate nuc. 

 int. cap. 

 'choroid pfex\ 

 3rd uent. 



thai. 



uent 

 chiasma 



Fig 169 —Diagrammatic Section across the 3rd Ventricle of the Adult to show the 

 ' Structures formed ill its Walls. 



capsule, are simply the enlarged upward continuations of the 

 tegmentum and crusta of the crura cerebri or mid-brain. From 

 Fig. 167, it will be seen that the optic thalamus is an upward 



