268 DETAILED SYNTHESIS. 



supply nutrition to the very active gray part, an almost 

 infinite number of capillaries must be woven through 

 it. Thus Ganglia require three tissues for their con- 

 struction : 



f Nervous T. \ ^& 

 _ 1 White. 



GANGLIA = j Smewy T 



[Secretory T. 



629. THE RELATIVE POSITIONS OF THE GRAY AND 

 THE WHITE TISSUES is not a uniform or essential mat- 

 ter ; sometimes the gray is external, sometimes internal, 

 sometimes interlaid ; thus the color of the Ganglia will 

 differ. 



630. THE SIZE OF GANGLIA varies from that of a pin's 

 head to the weight of a pound, and their form is equally 

 variable, evidently depending on the position in which 

 it is convenient to have them located. 



631. SOME OF THE GANGLIA HAVE free surfaces, 

 and some of them are merely surrounded by a con- 

 nective, sinewy tissue, supporting and retaining them 

 in place. 



632. Nothing is uniform, nothing therefore is ES- 

 SENTIAL IN GANGLIA except a proper number of perfectly 

 constituted nerve-cells connected with nerve-fibres, and 

 supplied with a sufficient quantity of good Blood to sus- 

 tain their nutrition, upon which their continued action 

 depends. 



Remark. We will now describe the different ganglia, when the 

 great facts of the preceding paragraph will become still more apparent. 



633. THE GANGLIA ARE CLASSED as Cranial or Brain- 

 al, Spinal, and Sympathetic. 



Remark. THE GANGLIA ARE OFTEN CLASSED as Cerebro-spinal and 

 Sympathetic, and the former subdivided : this is well except as to name, 

 which should be Cranio-spinal, for all the ganglia do not belong either 

 to the Cerebrum or Spinal cord, some forming the Cerebellum, &c. , 



629. What said of - ? 630. What is - ? 631. What do ? 682. What is f 

 633 How are ? 



