THE NERVOUS SYSTEM 



1429 



The superior brachium is associated with the vtsual apparatus. 

 The inferior brachium, though connected with the internal genicu- 

 late body, with which body the inner or commissural root of the 

 optic tract (commissure of Gudden) is also connected, is associated 

 with the acoustic apparatus. 



The superior brachium contains two sets of fibres, namel}^ 

 retinal fibres, derived from the outer root of the optic tract, and 

 (2) occipital fibres, from the cortex of the occipital lobe of the 

 cerebrum. , , ^, , , . 



The inferior brachium passes upwards from the lower quadn- 

 geminal body to the under aspect of the internal geniculate body. 



Optic Commissure 



■ _ Optic Nerve 

 Infundibulum 

 Tuber Cinereum 



Corpus Albicans 

 Mesial Root of Optic Tract 

 Lateral Root of Optic Tract .i'^. 

 External Geniculate BodyX. »• 



Locus Perforatus Posticus ^ 



Sixth Nerve 



Facial Nerve _ 



Pars Intermedia of Wrisberg. _" ~~ 

 Auditory Nerve.. 



Glosso-pharyngeal Nerve 



Pneumogastric Nerve 



Superficial Arcuate Fibres - 



Spinal Accessory Nerve-" 



First and Second Cervical Nerves ' 



Optic Tract 



Third Nerve 



Fonrth Nerve 



Motor Root of Fifth Nerve 



Sensory Root of Fifth Nerve 



Middle Peduncle of 

 Cerebellum 



Restiform Body 



Hypoglossal Nerve 



Anterior Median Fissure 



Decussation of the Pyramids 



Fig. 601. — The Medulla Oblongata, Pons Varolii, and Interpedunculak 



Region. 



C.C, Crus Cerebri ; P., Pyramid ; O.B., Olivary Body. 



which is a small oval mass on the lateral aspect of the mesen- 

 cephalon, under cover of the pulvinar of the optic thalamus. 

 Though the inner root of the optic tract is connected with the 

 internal geniculate body, the inferior brachium passes clear of it, 

 and the most of its fibres are traceable to the optic thalamus 

 through the tegmentum. 



Structure of Corpora Quadrigemlna. — The lower quadrigeminal body [col- 

 liculiis inferior B.) is composed of the following parts: 



1 . A central nucleus of grey matter. 



2. A dorsal layer of white matter. 



3. A ventral layer of white matter. 



The central grey nucleus consists of many multipolar cells and nerve-fibres. 

 The axons of the cells pass partly to the dorsal and partly to the ventral 

 layers of white matter. The nerve-fibres are derived from the lateral or 



