THE MEDULLA OBLONGATA. 547 



:ie substance of the medulla oblongata under cover of that projection. A small 

 :oportion of the fibres, however, are retained on the surface and travel upwards 

 wards the pons in the interval, which exists between the posterior border of the 

 ive and the roots of the vagus and glossopharyngeal nerves. 



The olive is a smooth oval projection which bulges out from the upper part of 

 ie lateral area of the medulla oblongata. Its long axis is vertical and is about 

 ilf an inch long. It marks the position of the subjacent nucleus olivaris inferior, 

 crumpled thin- walled sac of gray matter, which is separated from the surface only 

 Y a very thin layer of superficial white matter. 



Posterior Area of the Medulla Oblongata. In its inferior half, this district is 

 Dunded behind by the posterior median fissure, and in its superior half by the lateral 

 targin of the medullary part of the floor of the fourth ventricle of the brain. In 

 ont it is separated from the lateral area by the row of root-fila belonging 

 > the accessory, glossopharyngeal and vagus nerves. As in the lateral area, we 

 ^cognise an inferior portion and a superior portion, which appear continuous but 

 i reality are almost quite distinct the one from the other. 



The inferior part of the posterior area corresponds more or less closely with the 

 osterior funiculus of the spinal medulla. In the cervical region the posterior 

 iniculus is divided by a septum of pia mater into a medial fasciculus gracilis 

 nd a lateral fasciculus cuneatus. These are prolonged upwards into the medulla 

 blongata, and in the lower part of the posterior area they stand out distinctly, 

 nd are separated one from the other by a continuation upwards from the spinal 

 ledulla of the sulcus intermedius posterior. In the medulla oblongata the medial 

 f these strands is called the funiculus gracilis, whilst the lateral one is designated 

 he funiculus cuneatus. When they reach the level of the inferior part of the floor 

 f the fourth ventricle, each ends in a slightly expanded bulbous prominence, 

 "he swollen extremity of the funiculus gracilis is called the clava. This is thrust 

 ,side from its fellow of the opposite side by the opening up of the medulla 

 'blongata to form the floor of the fourth ventricle, and the central canal opens on 

 , he surface in the angle between the two clavse. 



The elongated prominences formed on the surface of the medulla oblongata by 

 hese two strands and their enlarged extremities are due to the presence of two 

 elongated nuclei or collections of gray matter which make their appearance 

 ubjacent to the strands, and represent the termini of these uppermost extensions 

 >f the spinal posterior root -fibres. These are termed respectively the nucleus 

 jracilis and nucleus cuneatus. [As it is the slenderness of the one nucleus and the 

 ,vedge-shape of the other in transverse section which gave rise to the terms gracilis 

 ind cuneatus respectively, it is clearly wrong to introduce the word funiculi into 

 l he B.N.A. terminology. The funiculi were named from the nuclei and not the 

 nuclei from the funiculi. ] 



But a third longitudinal elevation is also apparent on the surface of the inferior 

 part of the posterior area of the medulla oblongata. This is placed on the lateral 

 side of the funiculus cuneatus between it and the posterior row of nerve-roots 

 md it has no counterpart in the posterior funiculus of the medulla spinalis. It 

 is called the tuberculum cinereum. It is produced by a mass of substantia gelatinosa 

 3oming close to the surface and forming a bulging in this situation. Extremely 

 uarrow below, it widens as it is traced upwards, and finally ends in an expanded 

 xtremity. A thin layer of white matter, composed of longitudinally arranged 

 ibres, is spread over this district, and separates the substantia gelatinosa from the 



rface. These fibres constitute the tractus spinalis of the trigeminal nerve, which 

 . here assumes a superficial position as it descends in the medulla oblongata. 



Corpus Restiforme. The restiform body forms the upper part of the posterior 

 area of the medulla oblongata. It lies between the floor of the fourth ventricle and 

 ; the roots of the vagus and glossopharyngeal nerves. It is a large and prominent 

 rope -like strand, which inclines upwards and laterally, and then finally takes 



turn backwards and enters the cerebellum. It forms the great link of connexion 



jween the cerebellum on the one hand and the medulla oblongata and spinal 



dulla on the other, and consequently it is also called the inferior cerebellar 

 peduncle. A study of the surface of the medulla oblongata yields some important 



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