THE CEREBRO-SPINAL NEKVOUS SYSTEM. 495 



Gray Matter of the Medulla. To a considerable extent the gray mat- 

 ter of the medulla is a continuation of that in the spinal cord, but the 

 arrangement is somewhat different. 



The displacement of the anterior cornu takes place because of the 

 decussation of a large part of the fibres of the lateral columns in the 

 anterior pyramids passing through the gray matter of the anterior 

 cornu, so that the caput cornu is cut off from the rest of the gray 

 matter, and is, moreover, pushed backwards by the olivary body, to be 

 mentioned below. It lies in the lateral portion of the medulla, and ex- 

 ists for a time as the nucleus lateralis (Fig. 338, nl); it consists of a retic- 

 nlum of gray matter, containing ganglion cells intersected by white 

 nerve-fibres. The base of the anterior cornu is pushed more from the 

 anterior surface, and when the central canal opens out into the fourth 

 ventricle, forms a collection of ganglion cells, producing the eminence 

 of the fasciculus teres; from certain large cells, in it arise the hypoglossal 

 nerve (Fig. 338, XII.}, which passes through the medulla, and appears 

 between the olivary body and the anterior pyramids. 



In the fasciculus teres, nearer to the middle line as well as to the sur- 

 face, is a collection of nerve cells called the nucleus of that funiculus 

 (Fig. 339, nt}. The gray matter of the posterior cornu is displaced 

 somewhat by bands of fibres passing through it. The caput cornu ap- 

 pears at the surface as the funiculus of Rolando, whilst the cervix cornu 

 is broken up into a reticulated structure which is displaced laterally, 

 similar in structure to the nucleus lateralis. From the increase of the 

 base of the posterior cornu, the nuclei of the funiculus gracilis and fu- 

 niculus cuneatus are derived (Fig. 339, n.g, n.c), and outside of the latter 

 is an accessory nucleus formed (Fig. 339, n.c). Internally to these latter, 

 and also derived from the cells of the base of the posterio'r cornu and ap- 

 pearing in the floor of the fourth ventricle, when the central canal opens 

 are the nuclei of the spinal accessory, vagus, and glosso-pharyngeal 

 nerves. In the upper part of the medulla also, to the outside of these 

 three nuclei, is found the principal auditory nucleus. All the above 

 nuclei appear to be derived from a continuation of the gray matter of 

 the spinal cord, but a fresh collection of gray matter not represented is 

 interpolated between the anterior pyramids and the lateral column, con- 

 tained within the olivary prominence, the wavy line of which (corpus 

 dentatum) is doubled upon itself at an angle with the extremities 

 directed upwards and inwards (Fig. 339, o). There may also be a smaller 

 collection of gray matter on the outer and inner side of the olivary nu- 

 cleus known as accessory olivary nuclei. 



Functions. As in case of the spinal cord, the functions of the me- 

 dulla oblongata, like those of the spinal cord, may be considered under 

 the heads of: 1. Conduction; 2, Reflex action, or Reflection; and, in 

 addition, 3. Automatism. 



1. In conducting impressions the medulla oblongata has a wider ex- 

 tent of function than any other part of the nervous system, since it is 

 obvious that all impressions passing to and fro between the brain and 

 the spinal cord and all nerves arising below the pons, must be transmitted 

 through it. 



