534 | THE NERVOUS SYSTEM. 
side of a much larger strand of fibres in the medullary substance of the occipital 
lobe, viz. the optic radiation, 
On the inner wall two elongated curved elevations may be observed. The 
x SEPTUM 
LUCIDUM 
FORAMEN OF 
| THALAMUS 
i 
\ TAENIA 
Ya\| SEMICIRC: ff 
| CHOROID 
Wy PLEXus 
FIMBRIA 
HIPPOCAMP: 
EMINENTIA 
COLLATERALIS 
Fic, 396.—DIssection, to show the fornix and lateral ventricles ; the body of the corpus callosum 
has been turned over to the left. 
uppermost of these is termed the bulb of the cornu (bulbus cornu posterioris), and is 
produced by the fibres of the forceps major of the corpus callosum as they curve 
abruptly backwards from the lower part of the splenium of the corpus callosum into 
the occipital lobe. Below this is the elevation known as the calear avis. It varies 
greatly in size in different brains and is caused by an infolding of the ventricular 
wall in correspondence with the anterior calearine fissure on the exterior of the 
hemisphere. 
Descending Horn of the Lateral Ventricle (cornu inferius).—The descending 
horn is the continuation of the cavity into the temporal lobe. At first directed 
backwards and outwards, the descending horn suddenly sinks downwards behind 
the optic thalamus into the temporal lobe, in the centre of which it takes a curved 
course forwards and inwards to a point about an inch behind the extremity of the 
temporal pole. 
In the angle between the diverging posterior and descending horns the cavity 
of the ventricle presents an expansion of a somewhat triangular shape. To this, the 
name of trigonum ventriculi is sometimes given. 
The roof of the descending horn is formed for the most part by the tapetum of 
the corpus callosum. At the extremity of the horn the roof presents a bulging 
into the cavity. This is the amygdaloid tubercle, and it is produced by a super- 
