300 THE RHOMBENCEPHALON. 



The rubro-spinal tract is the crossed descending tract of 

 the red nucleus (Figs. 92 and 95). Running dorsal to the infe- 

 rior olive in the medulla it mingles with the fibers of the anterior 

 ascending cerebello-spinal tract. It is continued down the cord, 

 in the lateral column, to the lateral columna and center of the 

 gray crescent as far as the first lumbar segment (see pages 162, 

 276 and 358). 



Longitudinal Fibers of the Posterior Area. The longitudi- 

 nal fibers of the posterior area form many bundles ; and the bundles 

 are different in upper and lower medulla. The substantia reticularis 

 is small. The ventricular gray substance belongs to this area. 



The lower medulla contains: The funiculus gracilis, funic- 

 ulus cuneatus, tractus spinalis nervi trigemini and cerebello- 

 spinal tract, named from the posterior median fissure outward 

 (Figs. 94 and 96). In the upper medulla are: The restiform 

 body and the spinal tract of the fifth cerebral nerve at the surface ; 

 and the tractus solitarius in the interior (Figs. 92, 93 and 96). 



The funiculus gracilis is the superior end of the ascending 

 postero-medial column (GolPs column) of the spinal cord. Near 

 its extremity it expands and forms the clava, and then tapers off 

 and disappears along the side of the fourth ventricle. The clava 

 is due to the nucleus funiculi gracilis, in which the fibers of the 

 column end. The funiculus gracilis is composed of ascending 

 branches of the posterior roots of the spinal nerves, which enter 

 the cord below the seventh or eighth thoracic segment. 



Funiculus Cuneatus (Figs. 94 and 96). It is separated from 

 the posterior median fissure by the gracile bundle; and is the 

 continuation of the ascending postero-lateral column (Burdach's 

 column) of the spinal cord. It ends about the cells of the nucleus 

 funiculi cuneati and accessory nucleus funiculi cuneati, which 

 form the cuneate tubercle seen on the surface. The fibers of the 

 funiculus cuneatus are ascending branches of the posterior roots 

 of the spinal nerves. The nerves contributing to this column 

 are the cervical and the six or eight upper thoracic. The funiculi 

 gracilis and cuneatus carry to the nuclei of these columns common 

 sensations belonging to the tactile and muscular senses. Inter- 

 ference with these tracts produces ataxia. 



