876 THE NERVE SYSTEM 



2. The external or superficial arcuate fibres take origin (a) from the gracile 

 and cuneate nuclei and enter the restiform body of the same side; (6) from the 

 same nuclei of the opposite side, decussating in the raphe and sweeping ventrad 

 over the pyramid and olive, forming a thin layer over them and ultimately reaching 

 the restiform body. Many of these fibres are interrupted, on each side, in the 

 nucleus arcuatus, a thin, isolated lamina of gray substance lying on the ventral 

 aspect of the pyramid. 



The nucleus lateralis is seen in the lateral column (lower part of medulla ob- 

 tongata) as a diffuse gray mass lying between the gelatinosa Rolandi and the olive; 

 it gradually disappears cephalad. 



The nucleus intercalatus (of Staderini and Van Gehuchten*) forms the elongated, 

 wedge-shaped elevation in the medial triangle of the caudal portion of the ventric- 

 ular floor called the area plumiformis (p. 869); the nucleus derives its name from 

 its (intercalated) position between the hypoglossal and dorsovagal nuclei. Its 

 functional connections are not yet precisely known. 



A nucleus postremus has been described (J. T. Wilson) as lying subjacent to 

 the area postrema. 



The nucleus funiculi teretis lies close to the median sulcus in the altitude of the 

 acoustic strite, and seems to bear an intimate relation to these. 

 Summary of the Gray Masses in the Medulla Oblongata: 

 *Central tubular gray (in "closed" part). 

 *Gray floor of fourth ventricle (in "open" part). 

 *Gelatinosa Rolandi or gliosa. 

 ^Nucleus funiculi gracilis. 

 *Nucleus funiculi cuneatus. 

 *Nucleus funiculi cuneati accessorius. 

 *Nucleus lateralis. 

 ^Nucleus olivaris inferior. 

 ^Nucleus olivaris accessorius dorsalis. 

 *Nucleus olivaris accessorius medialis. 

 *Nucleus arcuatus. 



Nucleus nervi hypoglossi. 

 *Nucleus intercalatus. 

 *Nucleus postremus. 

 Nucleus vagi (alae cinereae). 

 Nucleus vestibularis (spinal division"). 

 *Nucleus funiculi teretis. 

 Nucleus ambiguus. 

 Nucleus tractus solitarii. 

 Nucleus tractus spinalis n. trigemini. 

 *Formatio reticularis. 



In the foregoing enumeration of the gray masses of the medulla oblongata, those 

 marked with an asterisk have been described above; the remaining structures 

 relate to the deep connections of the cranial nerves, and will be discussed in detail 

 under that head. 



Internal Structure of the Pons and Pars Dorsalis Pontis. Trans-sections of 

 the pons also pass through the tegmental part of the pons. To consider first the 

 internal structure of the pons proper (or pars basiiaris pontis) : The pons is com- 

 posed chiefly of (1) transverse fibres arranged in coarse bundles, (2) longitudinal 

 fibres gathered in compact bundles, and (3) diffusely scattered masses of gray 

 substance among the fibre bundles, the nuclei pontis. 



The transverse fibres, corresponding to the large size of the cerebellum, are more 

 abundant in man, relatively, than in any other animal. They form a massive 

 series of bundles coursing ventrad of the brain axis from one cerebellar hemisphere 



