ELEMENTAEY EXPERIMENTAL PHYSIOLOGY 



105 



the lower border of the petro-hyoid muscle. It is a small nerve, and 



not easily seen. Having traced the nerve so far, cut away the lower jaw 



and as much of the larynx as can safely be removed. Next cut away 



the mucous membrane which covers the base of the skull and upper 



vertebrae. You will thus expose on either side a broad muscle, the 



levator scapulae inferior. This 



muscle arises from the skull 



round the jugular foramen, 



and is inserted in the scapula. 



Unpin the frog, and hold the 



skull in the left hand, so that, 



while the skull is horizontal, 



the body hangs vertically. Cut 



through the levator muscle, 



and under the upper part of 



this muscle observe the 



vagus ganglion and the vagus 



and glosso-pharyngeal nerves. 



Trace the sympathetic nerve, 



which is marked by black 



pigment, along the 



vertebrae tO its junction with n * rves - Sym.= sympathetic 'nerve. G.P.: 

 J _ pharyngeal nerve. G.= vagus ganglion. (Gi 



the vagus ganglion. The 

 cardiac sympathetic fibres arise from the 3rd spinal nerve, and pro- 

 bably have their cell stations in the third sympathetic ganglion. 

 Pass a fine thread (by means of a sewing needle) under the sym- 



FKJ . 10 i._ Diagrara of the origin of the vago . 87mpa . 



. A. S.= l 



, 2,3, 4, 



urmpr e nerve (V.-S.)- L. A. S.= levator anguli scapulae 



upper muscle Aa=aorta 



first to ourth 



Glosso- 

 (Gaskell.) 



Fio. 102. Contraction of the frog's heart. The effect of weak stimulation of the 

 vago-syiupathetic nerve. The white line marks the duration of excitation. Note 

 the latent time, the acceleration and increased tone and the after-effect. The curve 

 should be read from left to right. (Pembrey and Phillips.) 



pathetic at the level of the large brachial (2nd spinal) nerve. Tie 

 it, and divide the nerve below the ligature. Pass a thread under 

 the glosso-pharyngeal and vagus nerves, but do not tie it. 



Place the frog again on the board, and record the heart by the 

 suspension method (slow rate of drum). With the interrupted current 



