12A 



A TEXTBOOK OF PHYSIOLOGY 



junction (G. 1, Fig. 33), upon the interauricular septum (G. 2, Fig. 33), 

 at the auriculo- ventricular junction (G. 3, Fig. 33). 



In regard to the distribution of ganglion cells in the ventricles, it 

 is generally conceded that they exist in the upper third of the ventricle, 

 the lower two-thirds being regarded as ganglion-free. 



The nerve endings in the heart are both receptor and effector. 

 As regards the sensory nerve endings (the depressor nerve), some ob- 

 servers hold that they do not supply the heart, but only the aorta; 

 others believe they end as tree-like expansions very like those found 

 in fascia and tendon in both the outer covering of the heart (epi- 

 cardium) and the lining membrane (endocardium). 



Gi 



FIG. 33. INTER-AURICULAR SEPTUM AND VENTRICLE SHOWING THE VAGUS NERVES 

 AND GANGLIA. (Hedon.) 



G. 1, Sinu-auricular or Remak's; G. 2, septal, or v. Bezold's; G. 3, auriculo-ventricular, 



or Bidder's. 



The effector nerve endings come from both the vagus and sympa- 

 thetic nerves, and it is stated that each heart fibre is surrounded by 

 a nervous network right down to the apex. 



Structure of the Bloodvessels. The whole vascular system is lined 

 within by a layer of flattened cells the endothelium. Each cell is 

 exceedingly thin, and cemented to its fellows by a wavy border of 

 an interstitial cement (protoplasm) substance. The endothelium 

 affords a smooth surface, along which the blood can flow with ease. 

 It Tests on a soft, thin film of connective tissue, the two together 

 forming the internal coat, or intima. Outside it there exists in the 

 arteries and veins a middle and an external coat. The middle coat, 

 or media, varies greatly in thickness, and contains most of the non- 

 striated muscle-cells, which in the smaller arteries and arterioles form 



