to the anterior end of the fornix, but neither their exact source of origin nor termination could be definitely determined.

(d) Posterior Commissure.-Some degenerated fibres were found in nearly all cases in the posterior commissure. Reference to these will again be made.

3. Projection Fibres: (a) Retro-Lenticular Group.-The largest group of degenerated fibres was in all cases traceable from the seat of injury through the corona radiata towards the internal capsule (see d. 1. fig. 3). On entering this system of fibres, the majority were found

Fig. 5.-Vertical section through anterior part of brain of marmoset vII., showing sites of degeneration :

d. 1. internal capsule.

d. 2. parieto-temporal fasciculus.

d. 3. anterior commissure.

to occupy the retro-lenticular segment of its posterior limb, some extending slightly forwards, however, between the posterior end of the lenticular nucleus and the optic thalamus. Certain of these fibres were seen to reach the capsule by piercing the back part of the lenticular nucleus. These, no doubt, correspond to the bundle which

Flechsig has recently described in the brain of an eight months' foetus, and which passes from the internal geniculate body to the anterior transverse temporal gyri perforating the putamen in its course. This bundle was medullated before those of the fillet, which are contributed to the posterior corpora quadrigemina.

The above retro-lenticular group descended with the capsular fibres, and was found to be distributed in the following ways. Many of its fibres entered the optic thalamus (see d. 3. fig. 4), and of these some were not traceable further. Others traversed this body, and

d. 1. and d. 2. as in fig. 5.

d. 3. external capsule.

d. 4. and 8. anterior commissure.

d. 5. corpus callosum.

d. 6. degenerations extending into opposite temporal lobe.

d. 7. opposite internal capsule.

appeared near the surface at a sulcus external to the anterior corpus quadrigeminus (see fig. 4.) Some of these latter entered the anterior tubercle; the remainder were continued backwards to enter the posterior

1 Flechsig, P., Zur Anatomie des vord. Seh-hugelstiels des Cingulum u. der Acusticus-Bahn. Neurol. Centralb. xvi. 7, p. 290.

2 Cf. Boyce," Contrib. to the Study of: I. Some of the Decussating Tracts of the Mid- and Inter-brain; II. Of the Pyramidal System in the Mesenceph. and Bulb." Phil. Trans. ser. B. vol. 188, pp. 218, 219.

tubercle of the corpora quadrigemina. Still others were continued into the internal geniculate body. These are probably identical with the similar fibres found by Boyce after removal of one hemisphere. Boyce considers, however, that they end chiefly on the opposite side. In my experiments this was not so, unless one regards these in the posterior commissure as belonging to the same system (vide infra). My observations therefore confirm those of numerous observers. In addition to the names already quoted, may be mentioned those of Dejerine, and of Ferrier and Turner, whose publications have appeared since the present research was undertaken.

Fig. 7.-Vertical section through same brain as figs. 5 and 6 but posterior to fig. 6:

d. 1., d. 2., d. 3., d. 5, and d. 6. same as in fig. 6.

d. 4. and d. 7. degenerations in tapetum.

d. 8. degeneration extending into optic thalamus.

It is interesting to note, at this stage, the existence of degenerated fibres in the posterior commissure (see d. 5. figure 8). These turned immediately downwards towards the dorsal grey nuclei of the

1 Dejerine, J., "Sur l'origine cert. et trajet intra-céréb. des fibres de l'etage inf. on pied du pédoncle cerebrale." Mem. de la Soc. de Biol. t. 5, p. 193-206.

2 Ferrier and Turner, W.A., "An experim. Research upon Cerebro-cortical afferent and efferent Tracts," Pro. Roy. Soc., lxxii., p. 1.

mesencephalon. They were no doubt continued from the capsular set of fibres, and would thus supply the cross link for a bilateral termination of the sets of fibres with which we are now dealing. That such bilateral method is the general plan of connexion between a given portion of the cortex and other masses of grey matter I have little doubt.

Lastly, a very definite fasciculus continued downwards in the internal capsule, traversing the sub-thalamic segment of this tract (see d. 1. fig. 7), and from thence passed into the outer part of the pes pedunculi. In the sub-thalamic region the degenerated fibres were found to occupy the posterior part, distributed amongst certain of the bundles of fibres into which the system is here subdivided (see

Fig. 8.-Vertical section through same brain as figs. 5, 6, and 7, but posterior to fig. 7; showing degenerations in :

d. 1. posterior part of internal capsule (subthalamic region).

d. 2. inferior longitudinal fasciculus.

d. 3. extending from tapetum into occipital lobe.

d. 4. tapetum of opposite side.

d. 5. posterior commissure.

d. 6. and 7. scattered through middle parts of internal capsules.
d. 8. traversing optic thalamus to reach corpora quadrigemina.

d. 1. fig. 8), but leaving others wholly free. These latter, which no doubt for the most part represent the projection system of the occipital lobe, were not always the most posteriorly situated. Quite a common arrangement was to find a small degenerated bundle

hindmost of all; then one or more larger bundles in which the fibres were normal; and in front of these the main set of degenerated fibres. The method of distribution was however subject to variation, and leads one to believe that the relative position of the various bundles is not absolutely constant.

1

2

The existence of a definite tract in the outer part of the pes pedunculi, descending from the temporal lobe, has been abundantly confirmed by many observers in recent as well as former years. Amongst later workers may be mentioned Dejerine, Van Gehuchten, Ferrier and Turner,3 Pusateri, and Gerwier, all of whom describe this tract. Van Brero stands alone in denying its existence. Nearly all of the authors mentioned consider that the bundle in question contains fibres from the temporal lobe only. Gerwier, on the other hand, assigns to it fibres from the occipital cortex as well. This view I can substantiate, both from the fact that amongst the degenerated fibres, numerous normal ones are found, and also from the results of experiments which I made on the occipital cortex in conjunction with Dr. Cecil Shaw, and published some years ago.

The fibres of this bundle when traced downwards were seen to enter a group of cells in the pons, situated external to the pyramidal bundles, and on the side of the lesion. The majority ended here, but some were found crossing in the trapezium to effect a connexion, no doubt, with the corresponding group of the opposite side. Thus, at this stage, a bilateral communication is again established. Gerwier also describes degenerated fibres crossing in the transverse bundles of the pons after lesions of the temporal cortex.

1 Dejerine, J., op. cit., p.

2 Van Gehuchten, "Contrib. a l'étude du faisc. pyram. Journ. de neurol. et d'Hypnol.," B. 1, p. 336-345; also 355-364.

3 Ferrier and Turner, W.A., op. cit.

4 Pusateri, E., "Contrib. allo studio dell' orig. del fascio pedunc. di Türck e del fascio long inf." Il Pisani, s. 141-154.

5 Gerwier (Herwer) A. W., "Ueber die Endigung. in d. Hirnrinde des lat. Bündels an. d. Basis d. Pedunc. cereb." Ueberschau über Psych. neurol. u. experim. Psych. H., 3, s. 222 (Ref. in centr. Bl. f. Nervhkde., 21. Jahrg., N.F., ix. 106, p. 687).

Van Brero, P.C.J. "La Termin. cort du faisc. latéral pédonculaire." Nouv Iconogr. de la salpêtriere. Année 9, No. 4, p. 206-222.

7 Shaw, C., and Thompson, W. H., "Desc. Degenerns. from Lesions of the cortex of the Occipital Lobe in Monkeys." Brit. Med. Journ., 1896, vol. ii.,

p. 630.

* Gerwier, op. cit.