AREAS OF THE MEDULLA OBLONGA1A 865 



dftr.ussation of the pyramids. Beyond this interruption the ventral fissure passes 

 cephalad to end at the ventrocaudal boroer of the pons in a recess called the 

 postpontile recess or foramen cecum. 



The dorsal or dorsomedian fissure (fissura mediana posterior} is of short extent 

 upon the medulla oblongata, for the neural cavity is here expanded into a rhom- 

 boidal fossa whose dorsal wall, profoundly atrophied, is represented only by a 

 delicate membranous lamina; the dorsal fissure rapidly becomes shallower as 

 it ascends, to cease at the caudal apex of the "fourth ventricle." 



Like the spinal cord, the surface of each half of the medulla oblongata is divided 

 into three longitudinal districts b1>fis.sures called the ventrolateral and dorsolateral 

 fissures. Of these, the latter only is a continuation of the fissure of the same 

 name in the spinal cord. 



The ventrolateral fissure (sulcus lateralis anterior) of the medulla oblongata 

 demarcates the ventral column (pyramid) from the lateral column as well as the 

 olive, and the roots of the hypoglossal nerve, arranged in linear order, emerge 

 from this fissure. 



(The ventrolateral fissure of the spinal cord becomes obscured as it ascends into the oblon- 

 gatal region, for cephalad of the emergence of the ventral roots of the first cervical nerve a 

 band of superficial arcuate fibres usually obliterates all traces of the furrow.) 



The dorsolateral fissure (sulcus lateralis posterior} of the medulla oblongata is 

 directly continuous with the same-named fissure of the spinal cord, and the root 

 bundles of the spinal accessory, vagus, and glossopharyngeal nerves are attached 

 along the bottom of this fissure. Unlike the dorsal roots of the spinal nerves. 

 the root bundles of these three cranial nerves are not all composed of afferent 

 fibres arising in extraneous ganglionic cells and entering the medulla oblongata, 

 for the accessory nerve is purely efferent and the vagus contains both afferent 

 and efferent fibres. 



Areas. The ventrolateral and dorsolateral fissures with their rows of nerve 

 fascicles divide the surface of the medulla oblongata on each side into three dis- 

 tricts which appear to be continuous with the three columns of the spinal cord; 

 ( they are not so in reality, however, owing to the rearrangement of the fibre tracts 

 and the central ganglionic mass in the myel-oblongatal transition. This portion 

 of the brain axis is sculptured into several eminences and depressions; of the emi- 

 Inences, some, like the olives, the tubercula cinerese, and the clavae, are due to the 

 .ccumulation of gray substance beneath the surface at that point; others, like the 

 yramids and restiform bodies, are due to the prominence at certain points of 

 he surface of the great nerve tracts. 



AREAS OF THE MEDULLA OBLONGATA. 



I. Ventral Area: 



Pyramid. 

 II. Lateral Area: 



(a) Lateral tract. 

 (6) Olive. 



III. Dorsal Area, marked by slight furrows dividing it into: 

 (a) Funiculus gracilis. 

 (6) Funiculus cuneatus. 

 (c) Funiculus lateralis and tuberculum cinereum. 



The last three structures mentioned appear to become fused cephalad to continue as the 

 sstiform body cr restis; in reality the restiform body is formed in a different manner. 



55 



