CHAPTER XXI 

 THE SPINAL CORD 



Membranes of the encephalon and spinal cord Cephalo-rachidian liquid Physiological 

 anatomy of the spinal cord Columns of Tiirck Crossed pyramidal tracts Anterior 

 ground columns Lateral bundles Ascending and descending cerebellar fasciculi 

 Direct cerebellar fasciculi Columns of Burdach Columns of Goll Directions of nerve- 

 fibres in the cord General properties of the spinal cord Relations of the posterior white 

 columns of the cord to muscular coordination Nerve-centres in the spinal cord Reflex 

 action of the spinal cord Reflexes in man. 



THE nervous structures contained in the cavity of the cranium and 

 in the spinal canal, exclusive of the roots of the cranial and spinal nerves, 

 constitute the cerebro-spinal axis. This portion of the nervous system 

 is composed of white and gray matter. The fibres of the white matter 

 act solely as conductors. The gray matter constitutes a chain of 

 ganglia, which act as nerve-centres, receiving impressions and gen- 

 erating impulses. Certain parts of the gray matter also serve as 

 conductors. 



The cerebro-spinal axis is enveloped in membranes for its protec- 

 tion and for the support of its nutrient vessels. It is surrounded to a 

 certain extent with liquid, and it presents cavities, as the ventricles of 

 the brain and the central canal of the cord, that contain liquid. The 

 gray matter is distinct from the white, even to the naked eye. In the 

 spinal cord the white substance is external and the gray is internal. 

 The surface of the brain presents an external layer of gray matter, the 

 white substance being internal. In the white substance of the brain, 

 also, are collections of gray matter. The white matter of the cerebro- 

 spinal axis is composed largely of fibres. The gray substance is 

 composed largely of cells. 



The encephalon is contained in the cranial cavity and consists of the 

 cerebrum, cerebellum, pons Varolii and the bulb, or medulla oblongata. 

 In the human subject and in many of the higher animals, its surface is 

 marked with convolutions by which the extent of its gray substance is 

 much increased. The cerebrum, the cerebellum and most of the enceph- 

 alic ganglia are connected with the white substance of the encephalon 

 and with the spinal cord. All the cerebro-spinal nerves are connected 

 with the encephalon and the spinal cord. 

 2N 545 



