MEDULLA OBLONGATA. 



725 



External to the corpora olivaria, are the restiform bodies, formed exclusively of 

 white matter and constituting the postero-lateral portion of the medulla. They are 

 continuous with the posterior columns of the cord. The restiform bodies spread out 

 as they ascend, and pass to the cerebellum, forming a great portion of the inferior 

 peduncles. 



Beneath the olivary bodies and between the anterior pyramids and the restiform 

 bodies, are the lateral tracts of the medulla, called by the French, the intermediary fas- 

 ciculi. These are composed of an intimate mixture of white and gray matter and have 

 a yellowish-gray color. They receive all that portion 

 of the antero-lateral columns of the cord which does 

 not enter into the composition of the anterior pyra- 

 mids. They are frequently considered as parts of the 

 restiform bodies, but they are peculiarly interesting, 

 from the fact that they contain the gray centre pre- 

 siding over respiration ; and, for that reason, we have 

 described them as distinct fasciculi. 



The posterior pyramids (fasciculi graciles) are the 

 smallest of all. They pass upward to the cerebrum, 

 without decussating, and are composed exclusively 

 of white matter. As they pass upward, they diverge, 

 leaving a space at the fourth ventricle. 



The fourth ventricle is in the medulla, and is 

 bounded above, by the valve of Vieussens and the 

 under surface of the cerebellum. In the lower part 

 of the floor of the fourth ventricle, are several trans- 

 verse fasciculi of white matter ; but the greatest part 

 of this portion is composed of a layer of gray sub- 

 stance. 



The two lateral halves of the posterior portion of 

 the medulla are connected together by fibres arising 

 from the gray matter of the lateral tracts, or inter- 

 mediary fasciculi, passing obliquely, in a curved 

 direction from behind forward, to the raphe in the 

 median line. There are also fibres passing from be- 

 fore backward, to form a posterior commissure, and 

 fibres arising from the cells of the olivary bodies, 

 which connect the gray substance of the lateral 

 halves. Commissural fibres also connect the gray 

 matter of the lateral tracts with the corpora dentata 

 of the olivary bodies, and the olivary bodies with the 

 cerebellum, their fibres forming part of the inferior 

 peduncles of the cerebellum. In addition, it is prob- 

 able that fibres, taking their origin from all of the 

 gray nodules of the medulla, pass to the parts of the 

 encephalon situated above. 



As far as the fibres of origin of the nerves are 

 concerned, it may be stated in general terms that a 

 number of the motor roots arise from the gray matter 



of the floor of the fourth ventricle, the roots of the sensory nerves arising from gray 

 matter in the posterior portions. 



Aside from purely anatomical demonstrations, the connection of the anterior pyra- 

 mids of the medulla with the corpora striata has been shown by pathological observa- 

 tions. It is well known that, when the connection between the nerve-centres and the 



FIG. 229. Anterior mew of the medulla 

 oblongata. (Sappey.) 



1, infundibulum ; 2, tuber cinereum ; 3, 

 corpora albicantia ; 4, cerebral pedun- 

 cle ; 5, tuber annulare ; 6, origin of the 

 middle peduncle of the cerebellum ; 7, 

 anterior pyramids of the medulla ob- 

 longata ; 8, decussation of the anterior 

 pyramids; 9, olivary bodies; 10, resti- 

 f orm bodies; 11, arciform fibres ; 12, 

 upper extremity of the spinal cord ; 13, 

 ligainentum denticulatum ; 14, 14, dura 

 mater of the cord ; 15, optic tracts ; 16, 

 chiasm of the optic nerves; 17, motor 

 oculi communis ; 18, patheticus ; 19, 

 fifth nerve; 20, motor oculi externus; 

 21, facial nerve; 22, auditory nerve; 2=3, 

 nerve of Wrisberg ; 24, glosso-pharyn- 

 geal nerve ; 25, pneumogastric ; 26, 26, 

 spinal accessory 27, sublingual nerve ; 

 28, 29, 30, cervical nerves. 



