THE DEEP CONNEXIONS OF THE CEEEBKAL NERVES. 593 



)rain-stem. This group comprises the hypoglossal nucleus, the abducens nucleus and, 



'.n the mesencephalon, the trochlear nucleus and part of the oculomotor nucleus. 



3ther motor nuclei of origin are present in the form of isolated clumps or columns 



)f gray matter, which lie at different levels in the medulla oblongata and pons 



n a more lateral and deeper situation. They are the nucleus ambiguus of the 



iccessory, vagus and glossopharyngeal, the facial nucleus, and the nucleus of 



]he motor root of the trigeminal nerve. From their position in the substantia 



>:eticularis of the medulla oblongata and pons they constitute a group to which the 



' name of lateral somatic nuclei is applied. 



In addition to these two columns of motor nuclei there is a third efferent 

 3olumn of splanchnic nuclei represented by the dorsal nucleus of the vagus and 

 glossopharyngeal nerves, and similar nuclei emitting sympathetic fibres into the 



ROOF-PLATE 



Splanchnic Terminal Nucleus. 

 ' Gustatory Nucleus. 



,Acoustico -Lateral 



Terminal Nucleus. 



Somatic Terminal 

 Nucleus. 



JO, Ear Vesicle. 



LAMINA] 

 BASALISJ 



Rssf-- 



Striped 

 Muscle 

 Sympathetic Ganglion - 



Sensory Ganglion. 



Somatic ----j 

 Efferent Nuclcus/jjVj 



Skin. 



ranchial 



trtped 



udcle. 



Visceral 

 Mucous Membrane. 



526. DIAGRAM REPRESENTING THE DIFFERENT KINDS OF COMPONENTS FOUND IN THE CEREBRAL 

 NERVES AND OF THEIR NUCLEI OF ORIGIN OR TERMINATION. 



facial and oculomotor nerves. It is possible some splanchnic efferent fibres may 

 pass into the trigeminal nerve. 



The different nuclei of origin of the efferent fibres which belong to the various 

 ( serebral nerves, both medial and lateral, are connected with the motor area of the 

 cerebral cortex by fibres of the cerebro-spinal tract of the other side, which enter 

 the nuclei and end in association with their cells. 



Nuclei Terminales. The general scheme of arrangement of the terminal nuclei 

 .ias already been explained (Fig. 526); its details will be further elucidated as 

 '^he various nerves are considered seriatim. 



The axons of many of the cells of the nuclei of termination enter the substantia 

 ^'eticularis as arcuate fibres, and, crossing the median plane, are carried upwards 

 in the substantia reticularis of the opposite side, to establish direct connexions 

 ,with the thalamus and, indirectly through it, with the cerebral cortex (Fig. 525). 



Others pass to the nuclei of motor nerves, to the cerebellum or other groups of 

 j aerve-cells, to form connexions necessary for the performance of reflex actions. 



39 



