Valentin on the functions of the nerves of the orbit / translated from the Latin by John F. France.

  • Gabriel Valentin
Date:
[1846]
Catalogue details

Licence: Public Domain Mark

Credit: Valentin on the functions of the nerves of the orbit / translated from the Latin by John F. France. Source: Wellcome Collection.

    16/40 page 12
    are effected by parts supplied from the inferior division of the motor oculi nerve ; and this proposition is coun¬ tenanced apparently both by human and comparative anatomy. We have elsewhere proved that the nucleated globules of the ganglia especially as¬ sist in automatic motion*. The motions of the iris, as we shall hereafter show more fully, are governed by nervous influence from two sources, the motor oculi, and the vagus and cervical sympathetic nerves. V/e have already said that contraction of pupil results from irritation of those fibres of the former which influence the iris ; and if these are paralyzed or impeded in their action, remarkable dilatation takes place. Diminution of the pupil arises from various causes; thus it ensues if the iris is mechanically irritated, as by escape of the aqueous humor, or lesion with a needle; and the circumstance hardly needs further explanation, the sensitive obviously exciting the motor ciliary fibres to reflex action. The pupil also contracts if both eyes are directed inwards, or inwards and downwards, or inwards and upwards; in other words, if the internal rectus, or internal and in¬ ferior recti, or internal rectus and inferior oblique, of both sides; or, which is the same thing, if the motor fibres of the inferior divi¬ sions of the third pair are simul¬ taneously in action. But it does not contract when the eye is volun¬ tarily turned straight upwards; audit actually enlarges upon strong exertion of the levator palpebrae superions : so that the remarkable contraction of this aperture, which is produced directly by the motor ciliary nerves, and indi¬ rectly by certain motor fibres of the third nerve, does not follow when the superior division of this nerve is in action. * Muck has observed in some beasts a branch sent from the ciliary ganglion to the inferior oblique and inferior rectus (De Gangl. Oph. &c. 1815): in the dog and cat it is distributed to the inferior oblique only ; in the weasel (mustela foina et putoria) to the rectus inferior likewise. I have myself always found in the sheep a large branch going from the ciliary ganglion to be united with the branches of the inferior division distributed to the inferior oblique and inferior rectus. The superior division, on the other hand, receives a twig from the long root before it enters the ciliary ganglion, a fact observed also by Faesbeck (Muller’s Archiv. 1839). It is evident, therefore, that the superior division of the motor oculi is augmented by branches of sensation only, and the inferior by filaments which have passed through the ganglion. The eflfect, however, is quite different when the motions of the eyes are harmonious instead of symmetrical : — I term harmonious motion of the two eyes, that which takes place in an analogous direction (as to the right or left) ; and symmetrical, that which is effected by analogous and similar mus¬ cles of opposite sides. The right eye being then directed outw’ards, and the left simultaneously inwards, or vice versa; that is, the external rectus of the right eye contracting, with the internal rectus of the left;—or again, the motor fibres of the sixth nerve of the right eye exerting their influence, together with those given to the internal rectus from the inferior division of the third nerve of the left,—no sympathetic con¬ traction of the pupil occurs. J. Miil- ler states the cause of this remarkable difference to be, the contrariety of the conditions; but 1 confess myself unable to perceive the force of his explana¬ tion. We have already shown that the inferior division of the motor oculi chiefly directs automatic, and the superior, voluntary movements. Now there is this law, as we shall see below, respecting ail automatic motions ; that different automatic parts, which receive branches either from the same nerve, or nerves close to one another at the nervous centre, and which I call syner¬ getic, move very readily in combina¬ tion. Another law is, that if an auto¬ matic part is primarily moved, the synergetic automatic parts are moved also ; but if a voluntary part and a single automatic one are moved to¬ gether in the first instance, the auto¬ matic synergetic ones remain pas¬ sive. Hence, when both eyes move in harmony, the voluntary external rectus of one, and the automatic internal rectus of the other, are ex¬ erted without any synergetic effect resulting: whereas if b^oth inter¬ nal recti contract at the same time (either in conjunction with the inferior recti, or inferior oblique, or not), the synerget'c automatic parts are likewise moved; that is to say, the iris is called into action and the pupil diminished. All the movements of the iris are automatic. Authors, indeed, speak of its voluntary motion ; but I have, by personal observation, obtained such acquaintance with this supposed power, as to be led to the foregoing conclusion on the subject. So-called voluntary
    digitised image 1
    digitised image 2
    digitised image 3