328 Journal Of Comparative Neurology. 



of greater length'than those of the other smaller nerves. AlsO 

 the dorsal branches of the 6th. nerve are relatively more abun- 

 dant than those of any of the four nerves below it. In this 

 respect, it more closely resembles the nerves anterior to it. In 

 order to study the relations of the dorsal branches to the other 

 parts of the nerve, a nerve with numerousfdorsal branches was 

 preferred. 



IV. Methods and Technique. 



The frog was chloroformed and the ovaries, if present, 

 were removed. Then the animal was weighed and its weight 

 and sex recorded. The viscera were next removed together 

 with such portions of the body-wall as would be in the way. 



Keeping the specimen moist in physiological salt solution, 

 the spinal cord was laid bare from the ventral side and then the 

 whole specimen placed ventral side up, in a petri dish contain- 

 ing salt solution, and resting upon the stage of a dissecting 

 microscope. With the aid of the dissecting lens, the nerve 

 roots were carefully detached from the cord and the cord 

 removed. The nerve trunk was then severed well beyond the 

 ramus communicans, and with small scissors the tissue into 

 which the dorsal branches enter so cut that the branches them- 

 selves would be severed, the danger of stretching or break- 

 ing them being thus avoided. Then with as little pulling as 

 possible, the whole nerve was removed and placed upon a nar- 

 row strip of glass. Making the dissection under the fluid 

 facilitates the operation considerably, in that it obviates any 

 tendency on the part of the nerve to tangle, and prevents adhe- 

 sion to the dissecting instruments. 



The strip of glass with the nerve adhering to it, was next 

 placed under the dissecting lens, and the roots, trunk, and dor- 

 sal branches straightened out and so arranged that the subse- 

 quent transverse sections of each could be most easily obtained. 

 Any remaining salt solution was then drained off and the strip 

 of glass with the nerve arranged upon it was put in i ^ osmic 

 acid for about ten minutes, or until the nerve was fixed suffi- 

 ciently to hold its shape. Then the nerve was carefully removed 



