1885.] of the Heart in Fishes, especially that of the Eel. 109 



ramify on its surface. The partial fixation of the ventricle by the 

 bands mentioned is probably in relation with this pecnliar mode of 

 blood-supply. There are generally two such vessels passing on ,to 

 each side of the ventricle. These vessels are arterial ; they are dis- 

 tributed to the outer part of the ventricular wall ; they do not supply 

 the whole thickness of the ventricular muscle. The greater part of 

 the ventricular substance is spongy (like the ventricle of the frog) 

 and is permeated by the venous blood passing through the heart ; the 

 outer part, however, is much more dense and compact in structure, 

 and is supplied with arterial blood by the special system of vessels 

 mentioned above. Veins are also seen upon the surface of the 

 ventricle ; they run upwards and backwards to terminate near the 

 mitral orifice, opening there into the tubular vessel which connects 

 the ventricle with the remaining parts of the heart. 



The ventricle is also attached to the bulbus arteriosus, to the 

 auricle, and to the sinus, by means of fibrous bands, which vary con- 

 siderably in number and arrangement. A series of such connexions 

 between the auricle and the ventricle exists around the mitral 

 orifice. 



The auricle is attached dorsally near the middle line by several 

 short thick bands, which pass to it from the dorsal aspect of the 

 pericardial chamber ; there are also some slender threads, which pass 

 to its ventral and lateral surfaces. The auricle is similarly con- 

 nected to a slight extent to the sinus, and the sinus has some con- 

 nexions with the lateral parts of the parietal pericardium. 



The sinus is placed dorsally, and is almost concealed by the over- 

 lying auricle. It receives, besides other vessels, the right and left 

 jugular veins, which enter it from above. 



Between the terminations of the two jugular veins, there is a part 

 of the sinus marked off from the rest by a slight fold — best dis- 

 tinguished when the heart is well filled with blood. This part is 

 physiologically distinct ; it may be termed the " inter jugular part of 

 the sinus." It becomes continuous with the dorsal wall of the 

 auricle. 



The ventral wall of the sinus passes on to be directly attached to 

 the ventricle at the mitral orifice. The proper auricular tissue does 

 not form a complete chamber ; it forms the lateral and dorsal parietes 

 of a chamber, the floor of which is chiefly made up by the prolonged 

 ventral wall of the sinus. (This prolonged ventral wall of the sinus 

 corresponds to the "basal wall" described by Gaskell in the tortoise 

 heart.) The auricle appears as a sort of appendage or diverticulum 

 bulging laterally and dorsally from the prolonged ventral wall of the 

 sinus. The auricle is not directly contiguous to the ventricle, but is 

 separated from the latter by a short intervening tubular vessel, some- 

 what resembling the canalis auricularis of the mammalian foetus. 



