200 



Prof. A. F. S. Kent. 



In close association with these nerve fibres there exist nerve cells, 

 occasionally single, often in groups of two or three, sometimes in large 

 numbers. Many of these cells are of great size, and in other particulars 

 remarkable in appearance. They are very markedly irregular in their 

 distribution, and may be scanty even where nerve fibres are abundant, 

 whilst in other situations they may be numerous. 



The exact function of these nerve cells is open to conjecture, and it is 

 therefore of interest to find them associated with other structures, the 

 connections of which may throw light upon their mode of action. 



The structures referred to are found lying in the connective tissue 

 between the auricular and ventricular muscle, and are of a type hitherto 

 undescribed in the heart. They consist of an elongated body, the first 

 indications of which in any series of sections is the appearance of two 

 or three nerve fibres lying amongst the fibrous tissue. In sections passing 

 directly from auricle to ventricle and taken vertically to the surface, these 

 fibres are as a rule cut transversely. If the series be followed the number 

 of fibres in the group is seen to increase, until ultimately a large number are 

 present. 



At this point some resemblance to an ordinary nerve trunk is presented, 

 and the diameter of the structure may be about 170 fi. 



The constituent fibres vary a good deal in size, ranging from about 3 fi to 

 about 12 /jb in diameter. A number of measurements gave the average 

 diameter of the most numeroiis fibres as about 7 /x. Connective tissue of 

 the fibrous variety is present in the bundle, but is principally developed at 

 the periphery, where in the greater portion of the length of the bundle, a 

 definite sheath is present, of considerable thickness, and composed of many 

 layers with large h r mphatic spaces lying between them. 



If the bundle, for the structure has now assumed the form of a bundle, 

 be followed further, a new constituent will be noticed to have made its 

 appearance. This new constituent is muscle, and it generally appears as a 

 small mass of tissue which stains more deeply than the rest of the bundle, 

 and is readily distinguished from the other constituents present. 



The muscle, after its appearance in the bundle, is generally to be found as 

 a fibre running longitudinally, or winding amongst the other tissues, and 

 showing a sharp differentiation into the darkly staining sarcostyles, and the 

 lighter sarcoplasm. The latter is generally arranged at the centre of the 

 fibre, whilst the sarcostyles occupy the periphery. 



One muscle fibre having appeared, others are soon noticeable, and the 

 number increases until a considerable portion of the bundle may be occupied 

 by muscular tissue. 



