MEDULLA OBLONGATA 



475 



The bilateral construction of the medulla oblongata is 

 indicated by the appearance of its exterior, for the antero- 

 median and postero-median sulci on the surface of the spinal 

 medulla are prolonged upwards on the anterior and posterior 

 surfaces of the medulla oblongata. 



The antero-median fissure, 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 



Optic chiasma 

 Optic tract 



Corpus geniculatum 

 laterale 



Corpus geniculatum 

 mediale 



Substantia perlorata 

 posterior 



Junction of pons and 

 brachium pontis 



Restiform body 

 Olive 



Decussation of 

 pyramids 



Optic nerve 

 Infundibulum 

 Tuber cinereum 

 Corpus mamillare 



Oculo-motor nerve 



(m.) 



Trochlear nerve (iv.) 



winding round 



cerebral peduncle 



Trigeminal nerve (v.) 

 Abducent nerve (vi.) 

 Facial nerve (VH.) 

 Acoustic nerve (vin.) 



Vagus and Glosso- 

 pharyngeal nerves 

 (ix. andx.) 

 Fila of hypo- 

 glossal nerve (xn.) 

 cut short 

 Accessory 

 nerve (xi.) 



nterior root of 

 first cervical nerve 



FIG. 192. Anterior aspect of the Medulla Oblongata, Pons, 

 and Mesencephalon of a full-time Foetus. 



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

 This intercrossing is termed the decussation of the pyramids. 

 Above the level of the decussation the furrow passes upwards 

 to the lower border of the pons. There it expands slightly, 

 and ends in a blind pit, termed the foramen ccecum. 



The postero-median fissure runs upwards for only half the 

 length of the medulla oblongata. Then the central canal, 

 continued upwards from the medulla spinalis, becomes the 

 fourth ventricle of the brain. As the canal expands dorsally 

 it pushes aside the Hps of the posterior median fissure till 



