TUI: f'i:iii-i;i,'n.si'i\.\r. \.\I8. 659 



It is worthy of remark that the properties of the nervous system, which 

 net in so important a manner on the organs of vegetative life, have no 

 direct influence on nutrition itself. Destruction of the nerves in a certain 

 region will certainly derange the nutrition of its tissues, in consequence of 

 the paralysis of the vessels, but it is not destroyed. There is an immense 

 rory of organised beings vegetables, for instance in which nutrition 

 is very active, and in which there is no nervous system. So that the 

 property which determines the essential phenomena of nutrition is indepen- 

 dent of nervous action : it is an attribute of living matter. 



SECOND SECTION. 



THE CENTRA i. Axis OF THE NERVOUS SYSTEM. 



TIIK cerebro-ttjitiHil n.rix is resolved, as we have said, into two principal 

 sections the spinal cord and the encepJtalon. We will study these two 

 [i<ii timis in succession, the spinal cord first, in order to facilitate our de- 

 scription, although that organ only holds the second place in a physiological 

 point of view. The protective parts of these two apparatus will, however, bo 

 lined before we proceed further. 



CHAPTER I. 



THE ENVELOPING AND PROTECTING PARTS OF THE CEREBRO-SPINAL 



AXIS. 



THE nn hro spinal apparatus is lodged, as we already know, in a bony caso 

 the *i>!n<il <-<ntal which is prolonged anteriorly by the cranial canty ; but 

 it is protected more immediately by three envelopes, which have received the 

 names of <lnrn mater, arachnoid, and >ia mater. 



THE BONY CASE THAT CONTAINS THE CEBEBBO-SPINAL AXIS. 



A knowledge of the bones which enter into the composition of this pro- 

 ve case, cannot bo acquired without also knowing the caso itself; so 

 that we dispense witli its special study here. We will allude, however, to 

 the succinct terms already employed in describing the xp'tnal canal, and in 

 -ame spirit of concision will also describe what has hitherto been 

 led- the cranial cavity. 



1. TJie Spinal (\inal. 



This canal communicates, anteriorly, with the cavity of the cranium. 

 Very wide at the atlas to receive the odontoid process, und allow ; 

 rotatory movements of the head which prevent the medulla being injured, 

 ;.inal canal suddenly contracts at the axis ; it expands a;,'ain at tlie end 

 of the cervical, and the commencement of the dor>al region, \\heru tho 

 medulla presents a greater volume, and the movements of tho spine arc very 

 e\t. iisive. Towards the middle of the hack, the spinal canal oilers its 

 smallest diameter, but on leaving tin's portion, and as far as the lumbo-sacral 



L U 2 



