Pig. 6. Dorsal Aspect of Fourth Ventricle. 



The Cerebellum has been removed by a section parallel with the floor of the 4th 

 Ventricle, so that the 3 Cerebellar Peduncles, strands which connect the Cerebellum with the 

 rest of the Central Nervous System, are seen on both sides in transverse section. 



1) Superior Peduncle conducting fibres chiefly to the Dentate Nucleus of the 

 Cerebellum. 



2) Middle Cerebellar Peduncle, connecting the Nuclei of the Pons with the Cerebellar 

 Hemispheres. 



3) Inferior Cerebellar Peduncle (Restiform Body) chiefly conducts to the Columns of 

 the Spinal Cord those fibres which passed to the Dentate Nucleus through the Superior 

 Peduncle. 



The Valve of Vieussens which lies across, between the Superior Cerebellar Peduncles, 

 has been cut and thrown to the left. 



The Facial Eminence (Colliculus Facialis) is produced b}' fibres of the Facial Nerve 

 which, after emerging from their cells, pass towards the floor of the 4th Ventricle and bend 

 at a right angle again, after a course of Vioth inch, to run backwards towards their nucleus 

 of origin. 



As the Nucleus of the Facial Nerve lies deep in the substance of the Pons and 

 Bulb, with many groups of cells extending upwards and downwards, it must be remembered 

 that this Nucleus is not at the floor of the 4th Ventricle and is accordingly represented 

 diagrammaticallv. 



The Nuclei of the other Cranial Nerves lie near the surface. The anterior part of 

 the Oculomotor Nucleus contains the fibres for the Sphincter of the Iris and the Ciliary 

 Muscles ; the posterior part contains the Fibres for the Extrinsic Muscles of the Eye. Immedi- 

 ately behind is the Nucleus of the IVth Nerve (Pathetic), the fibres from this pass to the Valve 

 of Vieussens where they decussate and on emerging ^wind round the Crura to reach the base 

 of the brain. The Nuclei of the \'th Nerve (blue) are partly sensory and partly motor; the 

 chief sensory Nucleus (pale blue) extends as far caudally as the 2nd Cervical Segment (De- 

 scending root of the Fifth Nerve), it is club-shaped with its broader end above. The chief 

 Motor Nucleus (dark blue) which is generally connected with the minor Motor Nucleus extends 

 upward into the region of the Anterior Corpora Quadrigemina. Although the shape of the 

 cells of this Nucleus are peculiar, it is probably motor. 



The function of the Locus Coeruleus is doubtful, its cells previously considered to be 

 sensory are now viewed as motor. 



The Nucleus of the Vlth Nerve lies directly under the floor of the 4th Ventricle in 

 the bend of the Facial Fibres described above. 



In the posterior part of the 4th Ventricle, which is separated from the anterior part 

 by the Striae Acusticae, a median grey and two lateral white triangular areae can be 

 delineated on either side. The grey area (Ala Cinerea) contains the Sensory Nucleus of IXth, 

 Xth and Xlth Nerves. The Motor Nucleus of these nerves (Nucleus Ambiguus) is marked 

 yellow; the Nucleus of their ascending root (Solitary Bundle of Meynert) which is not 

 indicated occupies a ventrolateral situation in relation to the Sensory Nucleus. 



The Sensory Nucleus is situated internal and at a deeper plane than the descending root 

 of the Vth Nerve The inner white triangle corresponds to the Hypoglossal Nucleus and the 

 outer to the Dorsal Nucleus of the Vlllth Nerve (Cochlear Portion). This Cochlear Portion has 

 another Nucleus (the Ventral Nucleus) situated along the outer border of the Inferior Cere- 

 bellar Peduncle. For the Vestibular Portion of the Vlllth Nerve there are two Nuclei shewn 

 in the figure (Deiteks' Nucleus and the Nucleus of the Descending Root of the Vlllth Nerve) 

 [Nucleus Tractus Spiralis Nervi Acustici]. Ziehen. 



