817 



of the trigeminus, it increases slightly in si/.e, due to t he progressive addition of fibres. 

 Its nucleus also increases slightly in bulk in approaching the region of the principal 

 motor nucleus of the trigeminus. The sensory nucleus (nucleus of termination) of 

 the trigeminus probably does not extend appreciably into the me-eiicephalon. 



The nuclei of the trochlear and oculomotor nerves form a practically continuous 

 column of nerve-cells extending close to the mid-line and ventral to the aquieduct us 

 cerebri. They are in line with the nuclei of origin of the abducens and hypoglossus, 

 and. like them, may be regarded as an upward continuation of the ventral group 

 of the cells of the ventral horn of the spinal cord. The portion of the column giving 

 origin to the oculomotor nerve is considerably larger than that of the trochlear. 



A transverse section through the inferior quadrigcminate bodies involves a por- 

 tion of the decussation of the brachia conjunctiva and the nuclei of origin of the 

 trochlear nerves, while a transverse section through the superior quadrigeminate 



FIG. (509. TRANSVERSE SECTION THROUGH THE INFERIOR QUADRIGEMINATE BODIES. 



CENTRAL GREY STRATUM 

 8TXATUX XO1TALB 



.vrr/.AT.v / /\I--/-:I:IOR 



' nl.l.K-l l.l'.-i 



AQUJKDUCTVB 



' 



VUCLSU8OF 

 HESENCEPHA- 



/,/''(/'/>'' '!:*!>- 

 IlfO] i:niii-nF 

 TJUOBIUNUB 



VtrCLSUSOF 



rum-ill. I-:.\H - - 



MI-:IHM. 



Tr/>l.\ .11. ~- 



MM ICULUS 



ni:.(i-inrM 



COKJVKO 

 TIVUH 



, 



HI-- HI: {i mi " ** 

 CONJVNCTIV1 



I'llXTKHUIR 



/:/: Efts OF 

 IXTERPEDUN- 



il I. 



NUCLEUS OF L.I TKK.t /, l.l-:.\l. \tSCUS 



\ LA TERAL LEMXISCUS (ACOUSTIC) 



MEDIAL LESfHISCUS 



LATKKM. 

 tCBBBtfCBPHALON 



BASIS Of CEREBRAL 

 FEDUSCLB 



SUPERFICIAL FIBRES OF POXS 



bodies passes through the red nuclei of the tegmentum and the nuclei of origin of the 

 oculomotor nerves. The latter section will also involve the brachia of the inferior 

 quadrigemmate bodies and the medial geniculate bodies connected with them. 

 The trochlear or fourth nerve is the smallest of the cranial nerves, and is the 



only one which makes its exit from the dorsal surface' of the brain, as well as the only 

 one whose fibres undergo a total decussation. Its nucleus of origin is situated be- 

 neath the inferior quadrigeminate bodies in the ventral margin of the central grey 

 substance, quite close to the mid-line and to its fellow nucleus of the opposite side. 

 and it is closely associated with the dorso-mesial margin of the medial longitudinal 

 fasciculus. Its fibres pass outwards and dorsalwards. curving around the margin 

 of the central grey substance, mesial to the niesencephalic root of the trigeminus. 

 As the mot curves towards the mid-line in the dorsal region just beneath the inferior 

 quadrigeminate bodies, it turns sharply and courses inferiorly to approach the surface 



