1882.] in the function of the cardiac muscle. 279 



with their accompanying ganglia pass between the sinus and the 

 ventricle. The thin inter-auricular septum arises along tbe median 

 line of this — so to speak — unbulged portion of the auricles. The 

 muscular tissue of this portion differs from that of the rest of the 

 auricles in not possessing any loosely reticulated structure, its 

 fibres being arranged closely together parallel to those of the 

 sino-auricular and auriculo- ventricular muscular rings. In fact 

 this band of tissue is exactly what would result if in an original 

 muscular tube containing nerve fibres and blood-vessels, in which 

 the muscle fibres were arranged circularly, a bulging of the mus- 

 cular tissues were to occur at one place which finally reached such 

 an extent as to flatten out the rest of the tube. 



This band of tissue with the auriculo-ventricular ring at the 

 one end and the sino-auricular at the other possesses rhythmical 

 properties next in importance to those of the sinus, and owing to 

 its external position it is easy by means of consecutive sections 

 or by clamping at different places to compare the rhythmical 

 property of one portion with that of another. 



In all cases the method of suspension as described in my 

 former papers was used, the fixed point being obtained either by 

 means of clamping or by holding the aorta firmly. In this way 

 all the different experiments are conducted under much the same 

 conditions. 



It is possible by means of the clamp or by section to remove 

 the sinus and adjacent parts without causing such an excitation 

 as is usually seen in the case of the second Stannius ligature, 

 so that the investigation need not be obscured by the production 

 of a series of beats which are simply caused by excitation and 

 are not spontaneous. In such cases we can compare efficiently 

 the nature of the spontaneous rhythm of auricle and ventricle 

 when the sinus only is removed, of ventricle and half the auricle 

 when the section is made in the middle of the inter-auricular 

 band of tissue already mentioned and of ventricle alone when 

 both sinus and auricles are removed. In all three cases the 

 resulting phenomena are the same in kind and vary only in 

 degree. In all three cases a longer or shorter standstill may 

 occur before spontaneous rhythm commences. Under the same 

 conditions however the length of this standstill is as a rule 

 greater the further away from the sinus the section is made. 



Also the spontaneous rhythm usually commences with beats 

 at long intervals from each other which steadily and gradually 

 quicken, until a certain definite regular rate is attained, which 

 continues for a long period without much alteration increasing 

 rather than diminishing in the course of time. A marked con- 

 trast is thus presented to the so-called rhythmical beats which 

 are seen in the frog's ventricle upon the application of the second 



