104 



PRACTICAL PHYSIOLOGY 



septum and cut it out, including its attachments to the ventricle. 

 Mount the septum in glycerine, and examine it microscopically. The 

 nerve fibres and ganglion cells will be apparent in the septum. 



Excitation of the Vagi, without dissection. Destroy the cerebrum 

 and spinal cord of a frog, leaving the spinal bulb uninjured. Stick a 

 needle electrode into each tympanic membrane. Record the beat of 

 the heart and faradise the spinal bulb ; inhibition is produced. 



01 



Fio. 100. Inter-auricular septum and ventricle showing the vagus nerves and 

 ganglia. G. 1 Remak's, G. 2 v. Bezold's, and G. 3 Bidder's. (Hedon.) 



Dissection for Exposing the Vagus in the Frog. 1 Lay the pithed 

 frog on its back, and cut through the skin and sternum. Pin out the 

 fore-limbs so as to pull the divided halves of the pectoral girdle widely 

 apart. Open the pericardium and divide the fraenum. From the 

 angle of the jaw on either side trace the thin band-like petro-hyoid 

 muscles. These muscles arise from the skull, and circle round to the 

 thyroid ' process of the hyoid. The petro-hyoids are crossed by two 

 white nerves, which are clearly visible. One, the glosso-pharyngeal, 

 curves round from the angle of the jaw, and disappears among the 

 muscles of the floor of the mouth. The other, the hypo-glossal, takes 

 the same direction, but lies nearer to the mid-line of the mouth. 



The vagus, dividing into its cardiac and laryngeal branches, lies at 



1 See also another method of dissection, p. 108. 



