120 ANATOMY. 



rical vertebra it curves forwards, outwards, and downwards, terminating in the 

 left subclavian vein at its junction with the internal jugular. 



Describe the Right Lymphatic Duct. It is about an inch long, termi- 

 nating in the right subclavian vein at its union with the internal jugular, and 

 draining the lymphatics of those parts which are not connected with the tho- 

 racic duct. 



THE NERVOUS SYSTEM. 



How is the Nervous System divided? Into the Cerebro-spinal, or 

 nervous system of animal life ; and the Sympathetic, or nervous system of 

 organic life. 



What is the Structure of the Nervous tissue? It is formed of two 

 substances essentially different from each other, the White or fibrous, and the 

 Gray or vesicular matter. Chemically these contain phosphorized fat, albumen, 

 and water. A third form, the Gelatinous, is yet a subject of disagreement 

 among authorities. 



Describe the White Nerve-matter. It is composed of a number of tubes, 

 each consisting of a central Axis- cylinder, surrounded by the White Substance 

 of Schivann, and this again enclosed in the tubular membrane, or Nerve-sheath. 

 The whole arrangement is precisely analogous to that of a submarine telegraphic 

 cable. A bundle of such tubes is invested by a covering, the Neurilemma, or 

 perineurium, and is called a Nerve, and is nourished by a minute capillary 

 system of blood-vessels. 



How do Nerves terminate ? Sensory nerves end peripherally as plexuses 

 in their end-organs in the tissues. Motor nerves end peripherally in muscles 

 as plexuses, or plates. Their central termination is not yet understood. 



Of what does the Cerebro-spinal system consist? Of the brain, the 

 spinal cord, the ganglia, and the cranial and spinal nerves. 



THE BRAIN. 



What are the Membranes of the Brain ? The dura mater, the arach- 

 noid, and the pia mater. 



Describe the Dura Mater. It is a dense fibrous membrane lining the 

 interior of the skull, and forming the internal periosteum of the cranial bones. 

 It is continuous with the dura mater of the spinal cord, and is attached to 

 many parts of the base of the skull. It presents the following for exami- 

 nation : 



Falx Cerebri, an arched process sent into the longitudinal fissure of the brain, 

 contains in its upper and lower margins the superior and inferior longi- 

 tudinal sinuses. 



