LECTURE II. 53 



tlrical, pursuing a slightly undulating course, 

 and being in a considerable degree transpa- 

 rent. He states also that they are larger 

 than the ultimate fibres of muscles. 



Microscopical observers also tell us, that 

 though the nervous fibrils in each packet 

 appear distinct, and may be separated from 

 each other in the manner already described, 

 yet they have nevertheless transverse com- 

 munications with each other. Each ner- 

 vous fibre has been supposed to be covered 

 by investing membranes similar to those of 

 the brain ; but this opinion is founded on 

 an analogy with what is observed in the 

 optic nerve, rather than on actual observ- 

 ation with respect to others. That they 

 have investing membranes is clear, and we 

 are told that we may dissolve the medullary 

 or nervous matter by an alkali, and leave 

 these investing membranes ; or on the 

 other hand, that we may dissolve the in- 

 vesting membranes by nitric acid, and leave 

 the medullary fibres. 



Having thus spoken of the chief cir- 



E 3 



