SHORT TRACTS.
z. Fibres passing from all parts of the cortex to the thalamus and, vice versa, from the thalamus to the cortex—tractus and or the peduncles of the thalamus. Such connections include : a. The cortex of the frontal lobe with the anterior end of the thalamus ; b. The cortex of the central convolutions and of the anterior part of the parietal lobe with the outer and inner thalamic, nuclei ; c. The cortex of the posterior part of the parietal and of the occipital lobes with the pulvinar ; d. The occipito-temporal lobe with the ventral and medial parts of the thalamus.
An important ascending tract from the thalamus to the cortex is the tegmental tract, or radiation. The fibres pass from the ventral region of the thala mus, partly through the in ternal capsule direct to the cortex and partly first through the lenticular nucleus, sub sequently joining the fibres following the internal capsule. The course of those trav ersing the lenticular nucleus is shown in Fig. 129 ; com pare also Fig. 154. Fibres pass also in the opposite direction, from the cortex to the ventral part of the thalamus. The tegmental path is also designated as the tradus 2. Fibres 'Sassing from the cortex of the visual centre to the superior colliculus and to the corpus geniculatum laterale and, in the opposite direction, from the lateral gen culate body to the cortex. The corpus geniculatum laterale and the pulvinar, together
with the superior colliculus, constitute the primary visual centre, the connection of these parts with the cortical visual centre within the occipital lobe forming the optic radiation of Gratiolet. In this connection it is to be noted, that the fibres to the cortex pass only from the corpus geniculatum laterale, the chief end-station of the tractus opticus, and from the pulvinar thalami, fibres from the superior colliculus to the cortex not being authenticated.
3. Fibres passing from the cortex of the auditory centre to the inferior colliculus and to the corpus geniculatum mediale and, reversed, from the latter to cortex. As in the case of the superior colliculus, so also in that of the inferior, the presence of a quad rigemino-cortical tract is unproven.
4. Fibres passing from the cortex (frontal lobe, regio opercularis) to the nucleus ruber.
5. The fornix passing, as the equivalent of a bundle of the corona radiata, from the hippocampus to the diencephalon, the fibres ending within the corpus mamillare.