(Coidimied from page 336) 



42 Transverse section of a central cell from a large strand of the right limb 

 of the atrioventricular bundle, containing an arteriole. This condition vi^as 

 probably attained by an adai)tation of the cell about a closely apposed blood 

 vessel. 



43 Transverse section of a smaller strand of the right limb of the atrioven- 

 tricular bundle. This shows the variable shape of the cells, and the enveloping 

 connective tissue capsule. Between the sarcolemma and the capsule a space 

 invariably occurs, perhaps of the nature of a lymphatic channel, but not lined 

 by endothelial cells. The serrated borders and the perinuclear clear spaces are 

 fixation artifacts. 



PLATE 4 



p:xplanation of figures 



44 (a, b, c, d, e) Various forms of cells from a macerated preparation of the 

 right branch of the atrioventricular bundle. The cells vary considerably in 

 form and size, but can all be referred to a fundamental spherical or polyhedral 

 form. In unstained preparations the paired nuclei are somewhat darker than the 

 cytoplasm, and are homogeneous in appearance. The cytoplasm appears granu- 

 lar, and denser peripherally. The myofibrils are barely discernible. They 

 occur in all portions of the cytoplasm, though more abvmdantly peripherally, 

 are very irregularly disposed, and are continuous from cell to cell. X 535. 



45 Transverse section of smaller terminal subdivision of the left limb of the 

 atrioventricular bundle (Purkinje fibers) showing the pericellular lymphoid 

 spaces and the connective-tissue capsular-stroma. 



46 Cell from area of transition of left limb of the atrioventricular bundle 

 to the Purkinje fibers. The cell, still enveloped by a capsule, has elongated 

 into a fiber of Purkinje. The cell is apparently in a contracted condition. Cen- 

 trally it contains a large sarcoplasmic area free of myofibrils. The cell con- 

 tains a few intercalated discs at the levels of displaced telophragmata. 



47 Transverse section of two adjacent Purkinje fibers. The myofibrils are 

 arranged in the form of delicate radial lamellae. The cells are enveloped by a 

 connective tissue membrane. 



48 Longitudinal section of transition area from atrioventricular bundle to 

 Purkinje fibers. The Purkinje fiber (cell) is surrounded by a lymphoid space and 

 contains a step-form of intercalated disc. It probably represents a fusion 

 product of two originally distinct cells. 



49 Transition area between atrioventricular bundle and myocardium of 

 moderator band. The upper portion of the illustration shows Purkinja cells, 

 the lower, myocardium with band-discs. In figure 50 are shown the cells of the 

 atrioventricular bundle which ends in the Purkinje fibers here shown. X 535. 



50 Group of cells from the atrioventricular bundle of the moderator band. 

 Intercellular bridges are conspicuous; these are composed of myofibrils passing 

 irregularly between adjacent cells. X 535. 



51 Portion of longitudinal section of muscle of moderator band, correspond- 

 ing to the Purkinje fibers of the myocardium. Intercalated discs are forming 

 in relation to the fused sarcolemmae of these three adjacent fibers. The form- 

 ing Purkinje fiber is here represented by three originally distinct cells. The 

 discs do not generally arise in the line of fusion but at angles to the fusion-area. 



338 



