CEREBRAL CONNEXIONS OF OPTIC NERVE. 517 
Cortical Connexions of the Optic Nerve.—The superior quadrigeminal body, 
the external geniculate body, and the pulvinar constitute the lower visual centres 
or terminal nuclei of the visual part of the optic tract. The higher visual 
centre is placed in the cortex of the 
occipital lobe of the cerebral hemisphere, 
| and the connexions between this and the 
’ 
; 
} 
lower centres are established by a large 
strand of fibres which runs in the central 
white matter of the hinder part of the 
cerebral hemisphere, and which constitutes 
the optic radiation. The optic radiation 
is composed both of corticipetal and cor- 
ticifugal fibres. The former arise as the 
_ axons of the cells in the external geniculate 
body and the pulvinar, around which the % 
retinal fibres end, and they terminate in ed 
the cortex of the occipital lobe. The 3 NS 
corticifugal fibres take origin in the cortex se, CORP.GEN.EXT, 
of the occipital lobe and end in the pul- 20 coRP/gr SAK 
pO 
PULVINARXS 
vinar and superior quadrigeminal body UAE 
eiemer and iurner) “hus formed, the  “SoRrcENINT- | 
optic radiation forms a conspicuous strand nvoul SG 
- (Figs. 397, p. 535; 400, p. 538; 409, p. 550), 
which, reaching the retrolenticular part of 
the internal capsule, sweeps backwards into 
the occipital lobe of the cerebral hemisphere 
on the outer side of the posterior horn of 
the lateral ventricle. Its connexions will 
be studied more fully at a later stage. 
WAyin au” 
Flechsig does not beheve that the pulvinar is 
an internode interposed in the path of the optic 
nerve as it proceeds towards the visual area of — 
the cerebral cortex. He states that he has not © LOBE 
been able to convince himself that any fibres of 
the optic tract end in the optic thalamus. 
gid 199 0 
Fic. 380.—DIaGRAM OF THE CENTRAL CONNEX- 
IONS OF THE Optic NERVE AND Optic TRaCcT. 
Other Connexions of the Lower Group of 
Visual Centres.—(1) The nuclei of the nerves which supply the muscles which move the 
eyeball would appear to stand in intimate connexion with the lower group of visual centres. 
Most probably this connexion is established through the posterior longitudinal bundle. As 
previously stated, Held believes that axons of certain of the cells of the superior quadri- 
_ geminal body enter this tract. (2) Through the mesial fillet, the superior quadrigeminal body is 
connected with the medulla and cord. 
THE PARTS DERIVED FROM THE TELENCEPHALON. 
CEREBRAL HEMISPHERES. 
The cerebral hemispheres form the largest part of the fully-developed brain. 
When viewed from above they form an ovoid mass, the broadest end of which is 
directed backwards, and the longest transverse diameter of which will be found in 
the vicinity of the parts which le subjacent to the parietal eminences of the 
cranium. The massive rounded character of the anterior or frontal end of each 
cerebral hemisphere constitutes a leading human characteristic ; but the hinder or 
occipital end is narrow and pointed, and is directed somewhat downwards. The two 
cerebral hemispheres are separated from each other by a deep mesial cleft, termed 
the great longitudinal fissure. 
Great Longitudinal Fissure (fissura longitudinalis cerebri)—In front and 
behind the great longitudinal fissure passes from the dorsal to the ventral aspect of 
the cerebral hemispheres, so as to separate them completely from each other. In 
its middle part, however, the fissure is interrupted and floored by the corpus 
callosum, a white commissural band, which passes between the hemispheres and 
