

)M POSITION AND CENTRAL CONNECTIONS OF CRANIAL NERVES 863 





Rolando and continues in this position lateral to the fasciculus cuneatus as far as 

 the upper part of the cervical region where it disappears. 



The cells of the sensory nucleus are of large and medium size and send their 

 axons into the formatio reticularis where they form a distinct bundle, the central 

 path of the trigeminal (trigennnothalamic tract), which passes upward through the 

 formatio reticularis and tegmentum to the ventro-lateral part of the thalamus. 

 Most of the fibers cross to the trigeminothalamic tract of the opposite side. This 

 tract lies dorsal to the medial fillet; approaches close to it in the tegmentum and 

 terminates in a distinct part of the thalamus. From the thalamus impulses are 

 conveyed to the somatic sensory area of the cortex by axons of cells in the thalamus 

 through the internal capsule and corona radiata. Many collaterals are given off 

 in the medulla and pass from the trigeminothalamic tract to the motor nuclei, 

 especially to the nucleus ambiguus, the facial nucleus and the motor nucleus of the 

 trigeminal. 



The somatic sensory fibers of the vagus, the glossopharyngeal and the facial 

 nerves probably end in the nucleus of the descending tract of the trigeminal and 

 their cortical impulses are probably carried up in the central sensory path of the 

 trigeminal. 



The mesencephalic root (descending root of the trigeminal) arises from unipolar 

 cells arranged in scattered groups in a column at the lateral edge of the central 

 gray matter surrounding the upper end of the fourth ventricle and the cerebral 

 aqueduct. They have usually been considered as motor fibers that join the motor 

 root, but Johnston claims that they join the sensory root of the trigeminal, that they 

 develop in the alar, not in the basal lamina, and that the pear-shaped unipolar 

 cells are sensory in type. 



The Trochlear Nerve (IV cranial} contains somatic motor fibers only. It supplies 

 the superior oblique muscle of the eye. Its nucleus of origin, trochlear nucleus, 

 is a small, oval mass situated in the ventral part of the central gray matter o f the 

 cerebral aqueduct at the level of the upper part of the inferior colliculus. The 

 axons from the nucleus pass downward in the tegmentum toward the pons, but 

 turn abruptly dorsalward before reaching it, and pass into the superior medullary 

 velum, in which they cross horizontally, to decussate with the nerve of the opposite 

 side, and emerges from the surface of the velum, immediately behind the inferior 

 colliculus. The cells of the trochlear nucleus are large, irregular and yellowish in 

 color. The nuclei of the two sides are separated by the raphe through which 

 dendrites extend from one nucleus to the other. They receive many collaterals 

 and terminals from the posterior longitudinal bundle which lies on the ventral 

 side of the nucleus. 



There are no branches from the fibers of the pyramidal tracts to these nuclei; 

 the volitional pathway must be an indirect one, as is the case with other motor 

 nuclei. 



The Oculomotor Nerve (/// cranial) contains somatic motor fibers to the Obliquus 

 inferior, Rectus inferior, Rectus superior, Levator palpebra superioris and Rectus 

 medialis muscles and sympathetic efferent fibers (preganglionic fibers) to the 

 ciliary ganglion. The postganglionic fibers connected with these supply the ciliary 

 muscle and the sphincter of the iris. The axons arise from the nucleus of the 

 oculomotor nerve and pass in bundles through the posterior longitudinal bundle, 

 the tegmentum, the red nucleus and the medial margin of the substantia nigra in a 

 series of curves and finally emerge from the oculomotor sulcus on the medial side 

 of the cerebral peduncle. 



The oculomotor nucleus lies in the gray substance of the floor of the cerebral 

 aqueduct subjacent to the superior colliculus and extends in front of the aqueduct 

 a short distance into the floor of the third ventricle. The inferior end is continuous 

 with the trochlear nucleus. It is from 6 to 10 mm. in length. It is intimately 



