THE MESENCEPHALON 833 



possible, in part at least, it is seen above that is it associated (1) directly with the special nerve 

 of equilibration, the vestibular; (2) with the optic apparatus by way of the thalamus, and (3) 

 with the afferent impulses from the general body, by way of the direct cerebellar and Gowers' 

 tracts, by way of the nuclei of the fasciculus gracilis and cuneatus, and the nuclei of termination 

 of the trigeminus, glosso-pharyngeal and vagus. It has been suggested that by way of these 

 latter paths the cerebellum deals especially with those general afferent impulses which arise 

 within the muscles of the body (neuro-muscular spindles, etc.) and which are grouped under the 

 name "muscular sense." The cerebellum can be considered as an enlarged and modified por- 

 tion of the grey substance of the spinal cord, receiving a greater number and variety of afferent 

 impulses and with them mediating more comprehensive and complicated reflex activities than 

 is possible with the less abundant grey substance of a given portion of the cord proper. 



SUMMARY OF PRINCIPAL STRUCTURES IN RHOMBENCEPHALON 



A. Gross Exterior. 



1. Medulla Oblongata (Myelencephalon). 



f Cerebellum I Hemispheres-lobes and lobules. 

 I I, Vermis — lobules and Imgula. 



2. Metencephalon \ Pons I Dorsal part (preoblongata). 

 ^ I Ventral part (pons proper). 



f superior — brachium conjunctivum. 

 Cerebellar peduncles \ middle — brachium of pons. 

 [ inferior — restiform body. 



3. Isthmus of Rhombencephalon. 



4. Fourth Ventricle and its Chorioid tela. 



5. Anterior and Posterior Medullary Vela. 



B. Grey and White Substance. 



1. Funiculus gracilis, nucleus of fasciculus gracilis, funiculus cuneatus, nucleus of fasciculus 

 cuneatus. 



2. Internal and external arcuate fibres, decussation of lemnisci, lemniscus, medial lemniscus, 

 lateral lemniscus. 



3. Cerebral peduncles, pyramidal fasciculi, pyramids, decussation of pyramids, arcuate 

 nuclei. 



4. Superficial and deep strata of pons, nuclei of pons, branchia of pons. 



5. Inferior olivary nuclei, cerebello-olivary fibres, thalamo-olivary tract, spino-olivary tract. 



6. Nuclei embohformis, globosus and fastigii (of the roof), and nucleus dentatus with bra- 

 chium conjunctivum of cerebellum. 



7. Central gelatinous substance and gelatinous substance of Rolando. 



8. Reticular formation. 



9. Hypoglossal nerve and nucleus of hypoglossal. 



10. Spinal accessory nerve and lateral nucleus. 



11. Vagus and glossopharyngeal nerves, nucleus of ala cinerea, sohtary tract and nucleus 

 of sohtary tract, commissural nucleus of ala cinerea, nucleus ambiguus, dorsal efferent nucleus 

 of vagus. 



12. Vestibular nerve — its superior nucleus (Bechterew), its medial nucleus (Schwalbe), 

 its lateral nucleus (Deiters), and the nucleus of its descending (spinal) root. 



13. Cochlear nerve, dorsal nucleus and ventral nucleus of cochlear, acoustic medullary striae, 

 nucleus of superior olive, trapezoid body, nucleus trapezoidei, lateral lemniscus, nucleus of 

 lateral lemniscus. 



14. Facial nerve and nucleus of facial nerve. 



15. Glosso-palatine nerve, nucleus of glosso-palatine and nucleus salivatorius. 



16. Abducens and nucleus of abducens. 



17. Trigeminus, "sensory nucleus" of trigeminus, spinal tract and nucleus of spinal tract 

 of trigeminus. 



18. Masticator nerve, chief nucleus and (so-called) mesencephahc nucleus and root of 

 masticator. 



19. Medial longitudinal fasciculus. 



20. Nucleus intercalatus, nucleus of median eminence, nucleus incertus. 



THE CEREBRUM 



1. THE MESENCEPHALON 



The mesencephalon or mid-brain is that small portion of the encephalon which 

 is situated between and connects the rhombencephalon below with the prosen- 

 cephalon above. It is continuous with the isthmus rhombencephah, and occupies 

 the tentorial notch, the aperture of the dura mater which connects the meningeal 

 cavity containing the cerebellum with that occupied by the prosencephalon. 

 Its greatest length is about 18 mm., and it is broader ventrally than dorsally. 

 Its dorsal surface is hidden by the overlapping occipital lobes of the cerebral hemis- 

 pheres. It consists of — ^(1) the lamina quadrigemina, a plate of mixed grey 

 and white substance which goes over lateralward and below into (2), the cerebral 



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