THE LEMNISCUS 



839 



the fibres (visceral efferent fibres) which terminate in the ciliary ganglion, axones from which 

 supply the two intrinsic muscles concerned, viz., the ciliary muscle and the sphincter iridis. 



The nucleus of the oculomotor is associated with the remainder of the optic apparatus — (1) 

 by way of the neurones of the superior quadrigeminate body with the optic tract (retina) and 

 it receives impulses from the occipital part of the cerebral cortex of the same and the opposite 

 sides, and probably from the motor cortex of the frontal lobe; (2) by way of the medial longitudi- 

 nal fasciculus with the nuclei of the trochlear and abducens (the latter making possible the co- 

 ordinate action of the lateral and medial recti for the conjugate eye movements produced by 

 these muscles), and with the nucleus of the facial (associating the innervation of the levator 

 palpebrse with that of the orbicularis oculi); (3) with the nuclei of termination of the sensory 

 nerves, especially the auditory, by way of the lateral lemniscus and medial longitudinal 

 fasciculus. It is probably connected with the cerebellum by way of the brachia conjunctiva 

 and red nuclei. 



Fig. 663. — Diagram of Longitudinal Section of Nucleus of Oculomotor Nerve. 



(After Edinger.) 



r^ni mis^u£^j^£sJer,-o^ 



Nucleus of posterior com- 

 missure and med. longit. 

 fasc. 



Medial longitudinal 

 fasciculus 



Ciliary muscles (a) and 

 sphincter of iris (b) 



Levator palpebrse 



Superior rectus 

 Medial rectus 



Inferior oblique 

 Inferior rectus 



Superior groupfnucleus 

 of Edinger and West- 

 phal) 



- - Inferior group 



The eminence representing the inferior quadrigeminate body proper consists 

 of an oval mass of grey substance, the nucleus of the inferior colliculus, containing 

 numerous nerve-cells, most of which are of small size. A thin superficial lamina 

 of white substance, the stratum zonale, forms its outermost boundary, and 

 fibres from the lateral lemniscus enter it laterally and from below (stratum 

 lemnisci). Near the lateral margin of the central grey substance occurs the 

 beginning of the inferior brachium, a bundle containing fibres to and from the 

 medial geniculate body and the inferior quadrigeminate body. 



The lemniscus in the mesencephalon is considered in two parts. The more 

 lateral portion of the lemniscal plate occuring in the pons has here spread 

 dorso-laterally, and occupies a position in the lateral margin of the section, and is 

 known as the lateral lemniscus, while the medial portion which remains practically 

 unchanged in the tegmentum is distinguished as the medial lemniscus. (See 

 fig. 660). In the upper portion of the lateral lemniscus occurs a small, scattered 

 mass of grey substance, the nucleus of the lateral lemniscus, in which many of its 

 fibres are interrupted. 



The upper and greater portion of the lateral lemniscus with its nucleus belongs to the 

 auditory apparatus, being connected with the nucleus of termination of the cochlear nerve, 

 chiefly of the opposite side. (See fig. 650.) A large part of the fibres of this portion terminate 

 iri the inferior quadrigeminate bodies. Many of the latter enter at once the nucleus of the body 



