MEDULLA OBLONGATA. 



543 



c:ner of each side wall of the third ventricle the small foramen interventriculare 

 ( .T. foramen of Monro) leads into the cavity of the corresponding cerebral hemi- 

 jhere, which is known as the lateral ventricle. 



MEDULLA OBLONGATA. 



The medulla oblongata is the continuation upwards of the medulla spinalis. 



is a little more than 25 mm. (one inch) in length, and it may be regarded as 



Binning immediately above the uppermost root of the first cervical nerve, or, 



Optic nerv 



Optic chiasma 



Optic tract 



pedunculi cerebri 



Infundibulum (cut) 



Tuber cinereum 

 ^ Corpus mamillare 



^Sitbstantia perforata po^erior 

 Oculomotor nerve 



Trochlear nerve 



Motor root of 

 trigeminal nerve 



Sensory root of 

 trigeminal nerve*"*" 



lusobliquus pontis *--_/ 



ma intermedius - 



Acoustic nerve 



Flocculus cerebelli ; 

 Chorioid plexus in the 

 apertura lateralis of 

 : the fourth ventricle 



Lateral recess of/ 

 fourth ventricle 



Abducens nerve 

 Facial nerve 



Acoustic nerve 

 ?~~Nervus intermedius 

 - Glossopharyngeal nerve 



Facial nerv 



Decussation of pyramids 



^/ hj """^ Vagus nerve 



Accessory nerve 

 Hypoglossal nerve 



^Spinal root of accessory nerve 

 First spinal nerve 



' 



FIG. 478. FRONT VIEW OF THE MEDULLA OBLONGATA, PONS, AND MESENCEPHALON OF A 

 FULL-TIME HUMAN FCETUS. 



)ughly, about the level of the foramen magnum. From this it proceeds upwards 

 i a very nearly vertical direction, and ends at the lower border of the pons. 

 A first its girth is similar to that of the spinal medulla, but it rapidly expands 

 3 it approaches the pons, and consequently it presents a more or less conical 

 i)rm. Its anterior surface lies behind the grooved surface of the basilar portion 

 f the occipital bone, whilst its posterior surface is sunk into the vallecula of the 

 arebellum. The medulla oblongata is a bilateral structure, and this is indicated 

 n the surface by the presence of anterior and posterior median fissures, on the 

 entral and dorsal surfaces respectively. 



The fissura mediana anterior, as it passes from the spinal medulla on to the 

 ledulla oblongata, is interrupted at the level of the foramen magnum by several 

 trands of fibres which cross the median plane from one side to the other. This 

 atercrossing is termed the decussation of the pyramids. Above this level the fissure 



