AREAS OF THE MEDULLA OBLONGATA 



873 



the pyramidal decussation. In consequence of this passage of white (crossed 

 pyramidal) fibres through its substance the ventral gray horn is broken up into a 

 coarse network, while one portion of it, tfie caput cornu, is entirely separated from 

 the rest; only a small portion of the base of the cornu remains intact close to the 

 ventrolateral aspect of the central canal. The caput cornu, thus separated, is 

 displaced -laterally, and comes to lie close to the caput cornu dorsalis, which has 

 also shifted its position. In consequence of this breaking up of the greater part 



NUCLEUS 

 GRACILIS 



; DORSOMEDlAM 



HEAD OF DORSAL HORN 

 BASE OF VENTRAL HORN 

 HEAD OF VENTRAL HORN 



FIG. 640. Transverse section of the medulla oblongata at the crossing of the lemnisci or fillets. (Testut.) 



of the ventral gray cornu by white fibres a coarse network is formed in the anterior 

 and lateral areas of the medulla oblongata, which is named the formatio reticularis. 

 The gelatinosa Rolandi (gliosa cornualis) of the dorsal horn is continued into 

 the oblongata, but becomes insignificant, relatively, in the pars dorsalis pontis. 

 The spinal root of the trigeminal nerve is in ectal relation with the gelatinosa 

 Rolandi; at higher levels the spinal root of the vestibular nerve intervenes. 



FLOOR OF FOURTH VENTRICLE 



NUCLEUS GRACILIS 

 NUCLEUS CUNEATUS 



BASE OF VENTRAL HORN 

 ROOT OF THIFACIAL CAPPING 

 HEAD OF DORSAL HORN 



VAGUS NERV 



HEAD OF VENTRAL HORN 



HYPOGLOSSAL NERVE 



LEMNISCUS VENTRAL PYRAMID 



FIG. 641. Transverse section of the medulla oblongata at the lower end of the olives. The roof of the 

 fourth ventricles is not represented. (Testut, after Duval.) 



Decussation of the Lemnisci (fillets}. A similar change, dorsad and cephalad of 

 the pyramidal decussation, is caused by the decussation of axone bundles arising 

 in the nuclei of the gracile and cuneate fasciculi (Goll and Burdach). At this 

 level the base of the dorsal gray cornu undergoes change in the form of two thick 

 dorsal peninsular outgrowths which form the nuclei of termination of the axones 

 in the gracile and cuneate fasciculi; externally these gray masses produce the emi- 

 nences of the clava and cuneate tubercle. The axones from these nuclei stream 

 mesad and cephalad in a series of concentric arches, decussating in the raphe 

 with the bundles of the opposite side to form the decussation of the lemnisci 1 or 



1 Also called "mesal lemnisci" in contradistinction to the "lateral lemnisci" of different origin. 



