Hardesty, Spinal Nerves of the Frog. 67 



2. The dorsal and ventral roots vary both in length for 

 the different nerves and in relative size for the same nerve. As 

 a result of the difference between the rate of growth of the 

 spinal cord and the canal in which it lies, the more caudal 

 nerves possess the longer roots, since in the frog the spinal gan- 

 glia always remain in the intervertebral foramena. The length 

 of the roots thus gradually decreases until, passing cephalad, 

 the roots of the Ilnd and 1st nerves are merely long enough to 

 reach at almost right angles their zones of exit and entrance 

 upon the cord. The relation between the size of the two roots 

 of a nerve is more constant than the relation between the size 

 of the roots of any two successive nerves. The most striking 

 and constant difference between the two roots is presented in 

 the 1st or hypoglossal, the dorsal root being not only relatively 

 but absolutely smaller than that of any other nerve. 



3. The distance between the spinal ganglion and the ra- 

 mus communicans {c, Plate VI) undergoes a very considerable 

 variation for the different nerves. As shown in the plate, this 

 distance decreases rapidly between the Vllth and Ilird nerves, 

 the ramus being given off much closer to the ganglion in case 

 of the IVth, Ilird, Ilnd and 1st nerves. 



The relative size of any two or three successive nerves can 

 often be observed as decidedly different in different frogs or in- 

 deed, on the two sides of the same individual. The Vllth, 

 Vlllth and IXth have been more often noticed as varying in 

 this respect. When the IXth is proportionately small, the 

 Vlllth is generally large and when the Vlllth is smaller than 

 usual, the Vllth and IXth appear more than ordinarily large. 

 Quite often the Vlth, Vllth, Vlllth and IXth nerves were 

 noticeably larger on one side than on the other of the same in- 

 dividual. In these cases, the larger nerves were most often on 

 the left side of the animal. 



IV. The Nerves Which Were Investigated. 



An enumeration of the fibers was made for all the spinal 

 nerves except the Ilnd and Xth. The Ilnd was neglected for 

 the time being, because of its large but very short roots, be- 



