ELEMENTAKY EXPERIMENTAL PHYSIOLOGY 



65 



CHAPTER XV. 

 THE CARDIAC NERVES AND GANGLIA. 



The Intra- cardiac Ganglia, and Nerves. The vago- sympathetic 

 nerves enter the sinus with the superior venae cavae, and form a plexus 

 there which contains many ganglion cells (Remak's ganglion). The 

 nerves pass on to enter the auricular septum, which also contains 

 ganglion cells (v. Bezold's ganglion). Leaving the septum the nerves 

 enter the auriculo-ventricular junction, where third groups of ganglion 

 cells lie (Bidder's ganglion). 



To see these structures (Fig. 65), forcibly inject the living heart with 

 osmic acid (1% sol.), passing the needle of the hypodermic syringe 

 into the auricle. The osmic acid almost 

 instantaneously fixes the heart in disten- 

 sion. Cut out the heart and place it in a 

 watch-glass of 1 % osmic. After 5 minutes 

 open the auricles under water, look for 

 the 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. 



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 peri- 

 cardium and divide the fraenum. From 

 the angle of the jaw on either side trace FIG. 65. -inter-auricuiar septum and 



& J f ventricle showing the vagus nerves 



the thin band-like petro-hyoid muscles, and ganglia. G. i Remak's, G. 2 v 



J Bezold's, and G. 3 Bidder's. (Hedon.) 



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 dis- 

 appears 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. 69. 

 E 



