640 SPECIAL PHYSIOLOGY. 



papillares and columnse carneae, and the latter, in the posterior musculi 

 papillares and columnge carneae. The spiral and interwoven arrange- 

 ment of all these layers, must assist the powerful and simultaneous con- 

 traction of the ventricular walls, and may perhaps explain the rota- 

 tory movement of the heart during each beat, to be hereafter noticed. 

 The structure of the right ventricle is similar, but less complete. 

 Internal to the fourth layer, the fibres of the one ventricle are alto- 

 gether independent of those of the other. The layers of the right 

 ventricle are continued into each other, not at the apex only, as in the 

 case of the left ventricle, but also along the whole length of the sep- 

 tum. The right ventricle is regarded, by Pettigrew, as a sort of seg- 

 ment of the left one, and he refers to the shape and perfection of struc- 

 ture of the latter, and also to the position, and the mode of develop- 

 ment, of the septum, from a protrusion of the anterior wall of the 

 single ventricle of the primitive heart, as according with this view. 



The ventricular fibres, in the hearts of the Mammalia generally, seem to be 

 arranged on the same plan as that of the human heart, and a correspond- 

 ence is observed in the disposition of these fibres in the Bird, Reptile, and Fish. 



The nutrient arteries of the heart are the two coronary arteries, 

 the first branches given off from the aorta ; they arise just beyond the 

 semilunar valves, wind round the auriculo-ventricular groove, and 

 give off two chief branches, which run along the furrows between the 

 ventricles. The cardiac veins end chiefly in a short trunk, named the 

 cardiac sinus, which opens into the back of the right auricle, and is 

 protected by the valve of Thebesius, already described ; this sinus is 

 interesting, as being the persistent portion of the lower end of the left 

 descending vena cava of the early embryo, the remainder of which 

 closes from the root of the neck down to this sinus, leaving only cer- 

 tain vestiges behind. Numerous small cardiac veins enter the right 

 auricle by separate openings. It has been supposed by some, that 

 the blood may pass directly from the cavities into interstices in the 

 tissue of the heart, and this appears to be the case in the heart of the 

 frog and of certain Fishes, in which only one ventricle exists, contain- 

 ing a uniform fluid ; but this could hardly occur in the hearts of the 

 warm-blooded Birds and Mammalia, in which there are two separate 

 ventricles, one containing dark or impure blood. In these, ample 

 provision exists, in proper arteries, capillaries, and veins, for a special 

 nutrient circulation. The lymphatics are superficial (Fig. 101) and 

 deep. The nerves of the heart are derived, on each side, from the 

 pneumogastric nerves, and from the sympathetic system. The former 

 give off cardiac branches from their trunks, and also from their re- 

 current laryngeal branches; whilst the latter give off sympathetic 

 cardiac branches from the cervical ganglia. The phrenic nerves send 

 offsets to the pericardium, and possibly a few fibres to the heart it- 

 self. The sympathetic and pneumogastric branches unite to form the 

 cardiac plexuses, from which small plexuses and branches proceed 

 along the coronary arteries. Certain important ganglia exist upon 

 the heart ; the ganglion of Wriaberg lies beneath the arch of the 

 aorta, and in animals, as in the calf and frog (Remak), others are found 



