MEDULLA OBLONGATA 



521 



medulla are prolonged upwards on the anterior and posterior 

 surfaces of the medulla oblongata. 



The antero-median groove, as it passes from the spinal 

 medulla on to the medulla oblongata, is interrupted, at the 

 level of the foramen magnum, by several strands of fibres 

 which cross the median plane from one side to the other. 

 This intercrossing is termed the decussation of the pyramids. 

 Above this level the furrow is carried upwards to the lower 



Optic chiasma 

 Optic tract 



Corpus geniculatum 

 laterale 



Corpus geniculatum 

 mediale 



Substantia perforat 

 posterior 



Restiform bod 



Olive 



Pyramid 



External 



arcuate fibres 



Decussation of- 

 pyramids 



Optic nerve 

 Infundibulum 

 Tuber cinereum 



!orpus mamillare 

 Oculo-motor nerve 

 '(in.) 



Trochlear nerve (iv. ) 

 winding round 

 cerebral peduncle 



Trigeminal nerve (v.) 

 Abducent nerve (vi.) 

 Facial nerve (VH.) 

 Acustic nerve (vin.) 



Vago-glosso-pharyn- 

 geal nerve (ix. and x.) 



Fila of hypo- 

 glossal nerve (xn.) 

 cut short 



Accessory 

 nerve (xi.) 



First cervical nerve 



FIG. 219. Anterior aspect of the Medulla Oblongata, Pons, and 

 Mesencephalon of a full-time Foetus. 



border of the pons. There it expands slightly, and ends in 

 a blind pit, termed the foramen ccecum. 



The poster o-median fissure is carried up for only half the 

 length of the medulla oblongata. Then the central canal of 

 the medulla spinalis becomes the fourth ventricle of the brain, 

 and as it expands dorsally it pushes aside the lateral lips of 

 the posterior median sulcus till the epithelium of its posterior 

 wall appears on the surface, in the triangular interval between 

 the diverging posterior columns of the medulla oblongata, 



