610 Dynamic Theory. 



the spinal nerves join the cord. A tract, called Clark's column, of 

 icular or gray matter is found at the inner side of the base of the pos- 

 terior horns of the spinal cord. It extends up and down the cord be- 

 tween the 9th dorsal and 7th cervical nerves, but the vesicles are more 

 abundant between the 9th dorsal and 3rd lumbar. From these Clark's 

 vesicles are traced fibres, which run into the cerebellum without break, 

 and which are called the direct cerebellar tracts ( dc, fig. 347 ). They 

 pass through the restiform tracts into the superior vermiform process 

 ( middle lobe ) of the cerebellum. These tracts, the posterior root 

 tracts ( pr ), and the columns of Goll ( G- ), are all afferent, or sensory. 

 The columns of Goll extend upward to the clavate nuclei in the medulla 

 oblongata, opposite the calamus scriptorius. In man they begin about 

 the middle of the dorsal region. In monkeys they commence as low 

 down as the lumbar region. They increase in size as they ascend. 



There are two pyramidal tracts, one direct, the other crossed. The 

 direct one is continuous with the pyramid in the medulla oblongata on 

 the same side. It is in the front part of the column next the median 

 fissure. ( Fig. 347, T.-) They are also called columns of Turck. As 

 they pass down the cord they finally decussate through the anterior 

 commissure of the cord by the time they reach the middle of the dorsal 

 region. The crossed pyramidal tract is a continuation of the opposite 

 pyramid in the medulla oblongata. It occupies the posterior part of 

 the lateral column of the cord. (Fig. 347, P.) 



CHAPTER LX. 



FUNCTIONS OF THE MEDULLA OBLONGATA. 



The functions of the medulla oblongata acting alone without the in- 

 terference of stimuli from the cerebrum, are, like those of the spinal 

 cord, purely reflex. It, however, is connected with a different set of 

 nerves, and consequently its specialties are different. All the cranial 

 nerves, except the first four, viz., the olfactory, optic, rnotores occu- 

 lorum, and the pathetic, have their roots in the medulla oblongata. The 

 first four also have more or less direct connection with it, and so have 

 the nerves of touch by way of the spinal cord. So that the reflex ac- 

 tions that may be excited through the medulla are much more varied 

 and complicated than those excited through the spinal cord alone. The 

 medulla is the center for the nerves controlling respiration and other 

 vital functions, from which circumstance it happens that the brain may 

 be removed from above it, and nearly the whole spinal cord from below, 

 without immediately destroying life. These functions proceed auto- 

 matically. 



