I.] THE FROG. 103 



canal and largely surrounded by the perigan- 

 gliomc gla?ids (cf. p. 32). 



c. Distribution of the spinal nerves. Follow this 

 on one side. 



a. The ist; examine it on that side upon which 

 the floor of the mouth is retained. It passes 

 at first outwards and then forwards and in- 

 wards, beneath the mylohyoid muscle, to be 

 distributed to the muscles of the tongue 

 {hypoglossal nerve). 



/?. The 2nd and 3rd \ meeting, on a level with 

 the end of the transverse process of the third 

 vertebra, to form the brachial nen^e. Follow 

 it to the arm. 



y. The 4th, 5 th, and 6th; each forming a long 

 trunk which passes back for a considerable 

 distance, for distribution to the body wall 

 and integument. 



8. The 7th, 8th, and 9th ; running parallel with 

 each other and the urostyle {lumbosacral 

 plexus), and finally becoming bound together 

 to form the iliac nerve for distribution mainly 

 to the hind limb. Follow this to the leg. 

 This plexus is liable to variation. 



€. The loth, a small nerve lying immediately 

 internal to 8 and close against the urostyle. 

 It enters into connection with the lumbo- 

 sacral plexus, and is distributed to some of 

 the lesser muscles of the posterior extremity 

 and parts adjacent. 



C Examine one of the middle spinal nerves 

 with care, under a hand lens if necessary. 



