768 



NEUROLOGY 



extends from the bottom of the fissure to the floor of the fourth ventricle. Further, 

 certain of the cranial nerves pass through the substance of the medulla oblongata, 

 and are attached to its surface in series with the roots of the spinal nerves; thus, 

 the fibers of the hypoglossal nerve represent the upward continuation of the 

 anterior nerve roots, and emerge in linear series from a furrow termed the 

 antero-lateral sulcus. Similarly, the accessory, vagus, and glossopharyngeal nerves 

 correspond with the posterior nerve roots, and are attached to the bottom of a sulcus 

 named the postero-lateral sulcus. Advantage is taken of this arrangement to sub- 

 divide each half of the medulla oblongata into three districts, anterior, middle, 

 and posterior. Although these three districts appear to be directly continuous 

 with the corresponding funiculi of the medulla spinalis, they do not necessarily 

 contain the same fibers, since some of the fasciculi of the medulla spinalis end in 

 the medulla oblongata, while others alter their course in passing through it. 



The anterior district (Fig. 679) is named the pyramid (pyramis medulla? oblongatae) 

 and lies between the anterior median fissure and the antero-lateral sulcus. Its 

 upper end is slightly constricted, 

 and between it and the pons 

 the fibers of the abducent nerve 

 emerge; a little below the pons it 

 becomes enlarged and prominent, 

 and finally tapers into the anterior 

 funiculus of the medulla spinalis, 

 with which, at first sight, it ap- 

 pears to be directly continuous. 



The two pyramids contain the 

 motor fibers which pass from the 

 brain to the medulla oblongata and 

 medulla spinalis, corticobulbar and 

 corticospinal fibers. When these 

 pyramidal fibers are traced down- 



Brachium 



pontis 

 cerebelli 





..a 



FIG. 679. Medulla oblongata and pons. 

 Anterior surface. 



Via. 680. Decussation of pyramids. Scheme showing pas- 

 sage of various fasciculi from medulla spinalis to medulla ob- 

 longata. a. Pons. b. Medulla oblongata. c. Decussation of 

 the pyramids, d. Section of cervical part of medulla spinalis. 

 1. Anterior cerebrospinal fasciculus (in red). 2. Lateral 

 cerebrospinal fasciculus (in red). 3. Sensory tract (fasciculi 

 gracilis et cuneatus) (in blue). 3'. Gracile and cuneate nuclei. 

 4. Antero-lateral proper fasciculus (in dotted line). 5. Pyra- 

 mid. 6. Lemniscus. 7. Medial longitudinal fasciculus. _ 8. 

 Ventral spinocerebellar fasciculus (in blue). 9. Dorsal spino- 

 cerebellar fasciculus (in yellow). (Testut.) 



ward it is found that some two-thirds or more of them leave the pyramids in 

 successive bundles, and decussate in the anterior median fissure, forming what is 

 termed the pyramidal decussation. Having crossed the middle line, they pass down 

 in the posterior part of the lateral funiculus as the lateral cerebrospinal fascic- 



