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TEXT-BOOK OF PHYSIOLOGY. 



The anterior column or pyramid is composed partly of fibers 

 continuous with those of the anterior column of the spinal cord (the 

 direct pyramidal tract), and partly of fibers continuous with those of 

 the lateral column of the cord of the opposite side (the crossed pyram- 

 idal tract), which decussate at the anterior portion of the medulla. 

 The united fibers can be traced upward to the pons, where they 

 disappear from view. 



The lateral column is composed of fibers continuous with those 

 of the lateral column of the cord. As the fibers pass upward, how- 

 ever, they diverge in several directions. The fibers of the crossed 

 pyramidal tract cross the median line, as previously stated, to enter 

 into the formation of the anterior column; the fibers of the direct 

 cerebellar tract gradually curve backward, and in so doing unite with 

 other fibers "to "form the restiform body, after which they enter the 

 cerebellum by way of the inferior peduncle. Situated between the 

 anterior pyramid and the restiform body is a small oval mass, the 

 olivary body, composed of both white and gray matter. 



The posterior column is composed largely of fibers continuous with 

 those of the posterior column of the cord. The subdivision of this 

 column into a postero-external (Burdach) and a postero-internal 

 (Goll) is more marked in the medulla than in the cord. The former 

 is here known as the funiculus cuneatus, the latter as the juniculus 

 gracilis. These two strands of fibers are apparently continued into 

 the restiform body. Owing to the divergence of the restiform bodies 

 a V-shaped space is formed, the floor of which is covered with epithe- 

 lium resting on the ependyma. At the upper extremity of the 

 funiculus cuneatus and funiculus gracilis, two collections of gray 

 matter are found, known respectively as the nucleus cuneatus and 

 nucleus gracilis. Around the cells of these nuclei many of the fibers 

 of the posterior column end in brush-like expansions. 



The Fillet or Lemniscus. From the ventral surface of the cu- 

 neate and gracile nuclei axons emerge which pass forward and 

 upward through the gray matter and decussate with corresponding 

 fibers coming from the opposite nuclei. They then assume a position 

 just posterior to the pyramids and between the olivary bodies. These 

 fibers thus form a new distinct tract, termed the fillet or lemniscus. 

 As this tract ascends toward the brain it receives additional axons from 

 the sensory end-nuclei of all the afferent cranial nerves of the opposite 

 side with the exception of the auditory. From the end-nuclei of the 

 auditory nerve new axons ascend as a distinct tract situated near 

 the lateral aspect of the pons. From their position these two separate 

 tracts have been termed the mesial and lateral fillets respectively. 



Before proceeding to a consideration of the functions of the 

 medulla oblongata it will be found conducive to clearness to sketch 

 the salient anatomic features of the parts anterior to it and their 

 relations one to another. 



