When the injuries inflicted on these tuber cles were deep, more or less general convulsive movements were produced ; if one tubercle were injured, the opposite side only was so affected. These convulsions were due to the lesion of the central parts of the medulla ob longata, with which the optic tubercles are in timately connected. A remarkable vertiginous movement was likewise caused, the animal turning to the side from which the tubercle had been removed. It does not appear that this rotation could be attributed to any special in fluence of the medulla oblongata, but rather to a state of vertigo induced by the partial destruc tion of vision ; for Flourens found that the same effects could be produced in pigeons by blindfolding one eye. The movements, how ever, were not so rapid, nor did they continue so long. And Longet saw the same movements in pigeons in which he had evacuated the hu mours of one eye.° It may be remarked, that deep injuries to the quadrigeminal tubercles are very likely to affect the only commissural connection between the cerebrum and cerebellum (procesnis cere belli ad testes), the integrity of which must doubtless be essentially necessary to ensure harmony of action between these two great nervous centres.
There are many instances on record in which blindness was coincident with pathological alteration of structure in one or both quadrige minal tubercles. In some of the cases where the lesion extended to parts seated beneath the tubercles, disturbed movements were observed, as in the experiments above related.
We are ignorant of the object of the exten sive connections of the optic tmcts with the tuber cinereum, the crura cerebri, and the cor pora geniculata; but these points are highly worthy of future inquiry, especially with re ference to the office of these last-named bodies, which is at present involved in much obscurity. Alany of the fibres of the optic tracts are un doubtedly commissural between the corres ponding points of opposite sides, and exist when those which form the optic nerves are deficient.
We see, then, in the quadrigeminal tubercles, centres, which, whatever other functions they may perform, have a sufficiently obvious rela tion to the optic nerves, the eye, and the sense of vision. This is clearly indicated by ana tomical facts, especially by those of coinpara tive anatorny, by the results of experiment, and by the phenomena of disease. These bodies may, therefore, be justly reckoned as special ganglia of vision ; and we are led to seek for similar centres in connection with the other senses. The olfactory processes seem very probably to perform a similar office in reference to the sense of smell. Their structure, their relation to the olfactory nerves, and their direct proportion of bulk to that of these nerves, and to the developement of the olfactory apparatus, place this question beyond all doubt. It is not so easy to determine the special ganglia of hear ing ; but the olivary bodies, or the small lo bules connected with the crum cerebelli called by Reil thellocks, may be referred to as bearing a sufficient close anatomical relation to the auditory nerve to justify our regarding either. of them as well calculated to perform this func tion. And, with respect to touch, the ganglia
on the posterior roots of the spinal and the fifth nerves may perhaps be considered in the same light ; for this sense being diffused so universally, in various degrees, over the whole surface of the body, and being seated in a great number of different nerves, would need ganglia in connection with all those nerves which are adapted to the reception of tactile impressions. The analogous sense of taste has its ganglia in those of the glosso-pharyngeal and the fifth.* The upper and posterior part of the mesoce phale has already been referred to, as being most probably that part of the brain which is most directly influenced by emotional excite ment. Dr. Carpenter appears to localize the seat of emotional influence more specially in the corpora quadrigemina, and refers to certain fibres, which he considers terminate in those bodies, as channels of emotional impulses. Although I am compelled to differ from this able writer in this limitation of the centre of emotion (so to speak), and am far from admit ting the existence of a distinct series of fibres for emotional acts, I nevertheless think that the arguments he advances are most applicable to that view which refers the influence of emotion to the grey matter of this entire region, which is brought into connection with the spinal cord by the fibres of the anterior pyramids, as well as probably through the continuity of the olivary columns and the posterior horns of the spinal grey matter.
Every one has experienced in his own person how the emotions of the mind, whether excited by a passing thought, or through the external senses, may occasion not only involuntary movements, but subjective sensations. The thrill which is felt throughout the entire frame when a feeling of horror or of joy is excited, or the involuntary shudder which the idea of im minent danger or of some serious hazard gives rise to, are phenomena of sensation and motion excited by emotion. The nerves which take their origin from the medulla oblongata, meso cephale, or crura cerebri, are especially apt to be affected by emotions. The choking sensa tion which accompanies grief is entirely refer able to the pharyngeal branches of the glosso pharyngeal and vagi nerves, which come from the olivary columns. The flow of tears which the. sudden occurrence of joy or sorrow is apt to induce inay be attributed to the influence of the fifth nerve, which is also implanted in the olivary columns, upon the lachrymal gland ; or of the fourth nerve, which anastomoses with the lachrymal branch of the fifth. The more violent expressions of grief, sobbing, crying, denote an excited state of the whole centre of emotion, involving all the nerves which have connection with it, the portio dura, the fifth, the vagus, and glosso-pharyngeal ; and even the respiratory nerves, which take their origin from the spinal cord, as the phrenic, spinal accessory, &c. And laughter, " holding both his sides," causes an analogous excitation of the same parts of the central organ and of the same nerves. The very different effect pro duced by the excitement of the same parts must be attributed to the different nature of the mental stimulus.