rgg FUNCTIONS OF THE THIRD CRANIAL NERVE. 



of accommodation for a near object, is to be regarded as an associated movement 



( 392, 5). 



Anastomoses In man, the nerve anastomoses on the sinus cavernosus with the ophthalmic 

 branch of the trigeminus, whereby it receives sensory fibres for the muscles to which it is distri- 

 buted {Valentin, Adamiik), with the sympathetic through the carotid plexus, and (?) indirectly 

 through the abducens, whereby it receives vaso-motor fibres (?). t . 



Varieties. In some rare cases, the pupillary fibres for the sphincter run in the abducens 

 (Adamiik), or even in the trigeminus {Schiff, v. Grafc). 



Atropin paralyses the intrabulbar fibres of the oculomotorius, while Calabar bean 

 stimulates them '(or paralyses the sympathetic, or both compare 392). 



Stimulation of the nerve, which causes contraction of the pupil, is best demonstrated on the 

 decapitated and opened head of a bird. The pupil is dilated in paralysis of the oculomotorius, 

 in asphyxia, sudden cerebral anwniia {e.g., by ligature of the carotids, or beheading), sudden 

 venous congestion, and at death. m . 



Pathological Complete paralysis of the oculomotorius is followed by (1) drooping ot the 

 upper eyelid (ptosis paralytica) ; (2) immobility of the eyeball ; (3) squinting (strabismus) out- 

 wards and downwards, and consequently there is double vision (diplopia) ; (4) slight protrusion 

 of the eveball, because the action of the superior oblique muscle in pulling the eyeball forward 

 is no longer compensated by the action of three paralysed recti muscles. In animals provided 

 with a retractor bulbi muscle, the protrusion of the eyeball is more pronounced ; (5) moderate 

 dilatation of the pupil (mydriasis paralytica); (6) the pupil does not contract to light; (7) in- 

 ability to accommodate for a near object. It is to be noted, however, that the paralysis may 

 be confined to individual branches of the nerve, i.e., there may be incomplete paralysis. 



[Squinting. In paralysis of the superior rectus, the eye cannot be moved upwards, and 

 especially upwards and outwards. There is diplopia on looking upwards, the false image being 

 above the true, and turned to the right when the left eye is affected (fig. 426, 3). Inferior 

 Bectus. Defect of downward, and especially downward and outward movement, the eye being 

 directed upwards and outwards. Diplopia with crossed images, the false one is below the true 

 image and placed obliquely, being turned to the left when the left eye is affected. Diplopia is 



Internal External Superior Inferior Inferior Superior 



rectus. rectus. rectus. oblique. rectus. oblique. 



Fig. 426. 



The black cross represents the true image, the thin cross the false image. The left eye is 

 represented as affected in all cases {Bristow). 



most troublesome when the object is below the line of vision (fig. 426, 5). Internal Bectus. 

 Defective inward movement, divergent squint, and diplopia, the images being on the same plane, 

 the false one to the patient's right when the left eye is affected. The head is turned to the 

 healthy side, when looking at an object, while there is secondary deviation of the healthy eye 

 outwards (fig. 426, 1). Inferior oblique is rare, the eye is turned slightly downwards and in- 

 wards, and defective movement upwards. Diplopia with the false image above the true one, 

 especially on looking upwards ; the false image is oblique, and directed to the patient's left 

 when the left eye is affected (fig. 426, 4).] 



Stimulation of the branch supplying the levator palpebral in man causes lagophthalmus 

 spasticus, while stimulation of the other motor fibres causes a corresponding strabismus spas- 

 ticus. The latter form of squinting may be caused also reflexly e.g., in teething, or in cases 

 of diarrhoea in children ; [the presence of worms or other source of irritation in the intestines of 

 children is a frequent cause of squinting]. Clonic spasms occur in both eyes, and also as in- 

 voluntary movements of the eyeballs constituting nystagmus, which may be produced by 

 stimulation of the corpora quadrigemina, as well as by other means. Tonic contraction of the 

 sphincter pupillse is called myosis spastica, and clonic contraction, hippus. Spasm of the muscle 

 of accommodation (ciliary muscle) is sometimes observed ; owing to the imperfect judgment of 

 distance, this condition is not unfrequently associated with macropia. 



[Conjugate Deviation. Some movements are produced by non-corresponding muscles ; thus, 

 on looking to the right, we use the right external rectus and left internal rectus, and the same 

 is the case in turning the head to the right, e.g., the inferior oblique, some muscles of the right 

 side act along with the left sterno-mastoid. In hemiplegia, the muscles on one side are paralysed, 

 so that the head and often the eyes are turned away from the paralysed side, i.e., to the side of 



