The Nervous System 215 



The outer membrane, the dura mater, is much thicker and 

 stronger than the others, and closely lines the inner surface 

 of the skull and forms a protecting covering for the brain. 



The arachnoid is a thin membrane which secretes a serous 

 fluid that keeps the inner 

 surfaces moist. 



The pia mater is a very 

 delicate vascular membrane 

 which covers the convolu- 

 tions, dips into all the 

 fissures, and even pene- 

 trates into the interior of 

 the brain. 



329. The Medulla Oblon- 

 gata. The medulla oblongata 

 is the enlarged upper part 

 of the spinal cord lying 

 within the cavity of the 

 skull. It is immediately 

 under the cerebellum and 

 forms the connecting link 

 between the brain and the 

 spinal cord. It is about an 

 inch and a quarter long, 

 and from one-half to three- 

 fourths of an inch wide at 



its upper part (Fig. 119). FIG. 118. Illustrating the General Ar- 

 The gray matter of the rangement of the Nervous System. 

 ,,,.,, .' (Posterior view.) 



medulla is broken up into 



masses which serve as centers of origin for various nerves. 



330. The Functions of the Medulla Oblongata. The 

 functions of the medulla oblongata are closely connected 

 with the vital processes. It is a great nerve tract for 



