THE ENDOCARDIUM. 



261 



extensively distributed throughout the muscular substance, occurring in 

 the form of freely communicating fissure-like spaces, lying between the 

 muscular bundles, and lined by epithelioid cells ; the mode of origin 

 being thus to a certain extent lacunar. 



The nerves given off by the cardiac plexuses appear rather small in 

 comparison with the bulk of the heart ; they are derived partly fi'om the 

 cerebro-spinal and partly from the sympathetic system (more especially 

 from the pneumogastric nerve, and from the cervical and superior thoracic 

 ganglia of the sympathetic nerve). Besides the larger ganglia in the 

 cardiac plexuses at the base of the heart, the nerves present minute 

 ganglia at different points along their course in its substance, first 



Fig. 179. — View of a Partial Dissec- Fig. 179. 



TION OF THE FiBRES OP THE ANTERIOR 

 ■WALL OF THE VENTRICLES IN A ShEEp's 



Heart, designed to show the differ- 

 ent DEGREES OF OBLIQUITr OF THE 



FIBRES (Allen Thomson). 



At the base and ajiex the superficial 

 layerof fibres isdisplayed : in the interven- 

 ing space, more and moreof the fibres have 

 been removed from above downwards, 

 reaching to a gi-eater depth on the left 

 than on the right side. «\ «', the 

 superficial layer of the right ven- 

 tricle ; 6', &', the same of the left 

 ventricle ; at 2 this superficial layer 

 has been removed so as to expose the 

 fibres underneath, which are seen to have 

 the same direction as the superficial ones 

 over the left ventricle, but d liferent over 

 the right ; at 3 some of these have been 

 removed, but the direction is only 

 sliglitly different ; 4, transverse or 

 annular fibres occupying the middle of the 

 thickness of the ventricular walls ; 6, 7, 

 internal fibres passing downwards towards 

 the apex to emerge at the whorl ; between 

 c, c, the anterior coronary or interventri- 

 cular groove, over which the fibres of the 



superficial layer are seen crossing ; in the remaining part of the groove, some of the 

 deeper fibres turn backwards towards the septum ; d, the pulmonary artery ; e, the 

 aorta. 



figured and described by Remak.* The larger nerves course obliquely 

 downwards on the surface of the ventricles beneath the pericardium, 

 crossing the direction of the superficial fibres, and giving off at intervals 

 branches into the muscular substance. 



Endocardium. — The cavities of the heart are lined by a thin mem- 

 brane continuous with the inner coat of the bloodvessels, with which in 

 general structure it for the most part agrees. A layer of flattened 

 epithelioid cells covers and lines the inner surface, and beneath this 

 the endocardium consists of connective tissue with a close network of 

 elastic fibres often passing into fenestrated membrane. Muscular 

 fibres are present in some parts. These are for the most part similar 

 to those -which compose the chief muscular substance of the heart. 



* Froriep's Notizen, 1S3S, p. 137 ; and Miiller's ArcMv, 18i4, p. 463, taf, xii. 



