THE CEREBRO-SPINAL, NERVOUS SYSTEM, 491 



in which it is applied as well as the condition of the nerve cells, the con- 

 nection between the cells being so intimate that a series of co-ordinated 

 movements may result from a single stimulation. Whether the cells 

 possess as well the power of originating impulses (automatism) is doubt- 

 ful, but this is possible in the case of 



(h.) Vaso-motor centres which are situated in the cord (p. 147), and of 



(i.) Sweating centres which must be closely, related to them, and 

 possibly in the case of 



(/.) The centres for maintaining the tone of muscles. 



The Nutrition (a) of the muscles, appears to be under the control of 

 the spinal cord. When the anterior motor nerve cells are diseased the 

 muscles atrophy. In the same way (b) the bones and (c) joints are 

 seriously affected when the cord is diseased. The former where the an- 

 terior nerve cells are implicated do not grow, and the latter are disorgan- 

 ized in some cases when the posterior columns are affected, (d) The 

 skin too evidently is only maintained in a healthy condition as long as 

 the cord and its nerves are intact. No doubt part of this influence 

 which the cord exercises over nutrition is due to the relationship which 

 it bears to the vaso-motor nerves. Within the cord are contained, for 

 some distance, fibres (a) which regulate the dilatation of the pupil, (b) 

 which have to do with the glycogenic function of the liver, (c) which 

 control the nerve-supply of the vessels of the face and head, (d) which 

 produce acceleration of the heart's action, and, in fact, all the other so- 

 called sympathetic functions (see Chapter XXI.). 



B. The Medulla Oblongata. 



The medulla oblongata (Figs. 335, 336) is a column of gray and 

 white nervous substance formed by the prolongation upwards of the 

 spinal cord and connecting it with the brain. 



Structure. The gray substance which it contains is situated in the 

 interior and variously divided into masses and laminae by the white or 

 fibrous substance which is arranged partly in external columns, and 

 partly in fasciculi traversing the central gray matter. The medulla ob- 

 longata is larger than any part of the spinal cord. Its columns are pyri- 

 form, enlarging as they proceed towards the brain, and are continuous 

 with those of the spinal cord. Each half of the medulla, therefore, may 

 be divided into three columns or tracts of fibres, continuous with the 

 three tracts of which each half of the spinal cord is made up.' The col- 

 umns are more prominent than those of the spinal cord, and separated 

 from each other by deeper grooves. The anterior, continuous with the 

 anterior columns of the cord, are called the anterior pyramids; the pos- 

 terior, continuous with the posterior columns of the cord, with the ad- 

 dition of the funiculusof Eolando on each side (Fig. 337, fR), are called 



