FUNCTIONS OF THE FOUETH CEANIAL NEEVE. 



589 



the brain on which the lesion occurs. This is called -' conjugate deviation" of the eyes, with 

 rotation of the head and neck. If the right external rectus be paralysed from an affection of 

 the sixth nerve, on telling the patient to look to the right it will be found that the left eye will 

 squint more inwards even than the right eye, i.e., owing to the strong voluntary effort, the 

 muscle, the left internal rectus which usually acts along with the right external rectus, con- 

 tracts vigorously, and so we get secondary deviation of the sound eye. Similar results occur 

 in connection with paralysis of other ocular muscles. ] 



Corpus (anticum 

 quadri- J. 

 geminiua ( posticum 



Conarium or pineal gland. 



Brachium conjunctivum anticuin. 



Brachium conjunctivum 

 posticum. 



Middle cerebellar 

 peduncle. 



Corpus geniculatum 

 medial* 



Pedunculus cerebri. 



ad corpora quadri-^ 

 gemma, or 



superior cerebellar 

 peduncle. 



- ad medullam oblon- 

 uatam, or interior 



cerebellar 

 peduncle. 



Crus 

 cerebelli 



Accessorius nucleus 



Funiculus cuneatus 

 ( l'art of restiform body). 



Funiculus gracilis 

 (Posterior pyramid). 



Fig. 427. 

 Medulla oblongata, with the corpora quadrigemina. The numbers IV-XII indicate the 

 superficial origins of the cranial nerves, while those (3-12) indicate -their deep origin, i.e., 

 the position of their central nuclei ; t, funiculus teres. 



346. IV. NEEVUS TKOCHLEABIS. Anatomical. It arises from the valve of Vieussens, 

 i.e., behind the fourth ventricle, but its fibres pass to the oculomotorius from the trochlearis 

 nucleus, which is to a certain extent a continuation of the anterior horn of the spinal cord (fig. 

 427). It passes to the lower margin of the corpora quadrigemina, pierces the roof of the 

 aqueduct of Sylvius, then into the velum medullare superius, and after decussating with the 

 root of the opposite side behind the iter, it pierces the crus at the superior and external border 

 (fig. 428). Its fibres cross between its nucleus and its distribution. It has also an origin from 

 the locus ccsruleus. The root of the nerve receives some fibres from the nucleus of the abducens 

 of the opposite side. Physiologically, there is a necessity for a connection between the centre 

 and the cortical motor centre for the eye muscles. 



