I.] THE FROG. 103 



canal and largely surrounded by the perigan- 

 glionic glands (cf. p. 32). 



c. Distribution of the spinal nerves. Follow this 

 on one side. 



u.. The 1 st; 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 nerve. 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 (lumbo-'sacral 

 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. 



e. The 10th, 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. 



£. Examine one of the middle spinal nerves 

 with care, under a hand lens if necessary. 



