HEART. 



593 



over a wider surface at this their upper in- 

 sertion. I have been more particular in 

 describing this part of the heart, as this ar- 

 rangement of the fibres appears to me to be 

 intimately connected with the production of 

 the tilting motion of the heart. The fibres 

 which occupy the upper part of the anterior 

 surface of the left ventricle, as well as those 

 occupying the upper part of the posterior 

 surface (nearer the base than those bands 

 already described as passing from the ante- 

 rior surface), partly dip into the interior of 

 the left ventricle as they wind round it, 

 partly pass in at the posterior longitudinal 

 groove to assist in forming the septum, while 

 other strong bands, more particularly near the 

 base, cross this groove and dip into the interior 

 of the right ventricle. In the human heart 

 I have stripped off pretty strong superficial 

 bundles from the upper part of the posterior 

 surface of the left ventricle over the posterior 

 longitudinal groove, and over the surface of 

 the right ventricle as far as the anterior longitu- 

 dinal fissure, into which they dipped. In 

 stripping off the fibres from the posterior and 

 anterior surface of the right ventricle at this 

 stage of the dissection, part of them disap- 

 pear in their course around the ventricle, where 

 they dip in to assist in forming the interior; 

 others proceed as far as the anterior groove 

 before they dip inwards; while part of the 

 fibres which arise from the conus arteriosus 

 cross the upper part of the anterior fissure 

 upon the anterior surface of the left ventricle, 

 where they pass into the interior of the left 

 ventricle. These fibres, crossing the anterior 

 surface of the right ventricle, and which dip 

 in at the anterior fissure, form the inner sur- 

 face of the septum of the right ventricle. On 

 tracing those fibres which dip inwards at so 

 many different points, they are observed to rise 

 upwards to the tendinous rings either directly 

 or indirectly through the medium of the chordae 

 tendinea?. In following the fibres in this man- 

 ner we perceive the intimate connexion that 

 exists between the two ventricles, and that their 

 contraction must be simultaneous. We also 

 see that comparatively few fibres cross the 

 anterior longitudinal groove except near the 

 base, while large bundles of fibres cross the 

 posterior groove. \Vhen these fibres crossing 

 the two grooves have been torn away, the two 

 ventricles become detached from each other. 

 By this time the apices of both ventricles have 

 been opened. 



On examining the deeper fibres (which oc- 

 cupy that part of the heart near the base), they 

 are seen to form a series of curved bands, of 

 one of which Jig. 275 is a representation. 

 These bands are imbricated, the lower disap- 

 pearing by its internal extremity below the 

 higher, so as to be inserted by that extremity 

 into the tendinous rings at a point more in- 

 ternal than the corresponding extremity of the 

 higher bands. Some of these bands are com- 

 mon to both ventricles, others belong exclu- 

 sively to one. The fibres of the right ventricle 

 become very complicated where they form the 

 conus arteriosus and fleshy pons between the 

 VOL. n. 



Fig. 275. 



pulmonary artery and right auriculo-ventricular 

 orifice. The fibres of the left ventricle are 

 stronger and coarser than those of the right 

 ventricle, while those of the conus arteriosus 

 are still firmer than those on the lower part of 

 the right ventricle.* " There do not occur in 

 any part of the heart cellular sheaths or tenr 

 dinous aponeuroses dividing bundles of fibres 

 as separate muscular fasciculi. Although a 

 complex it is not a compound muscle, and 

 does not consist of a number of distinct bellies 

 or heads. The only thing approaching to this 

 structure are the columnar and a strong mus 

 cular stay between the peripheral and septal 

 wall of the pulmonic ventricle, and the re- 

 ticulated texture on the inside of the ventricles, 

 much more conspicuous in man than in oxen." 

 " Many fibres are attached to each other by 

 agglutination or in a manner not easily under- 

 stood." " Many fibres bifurcate, and the di- 

 vided fibres follow different directions : or two 

 fibres from different parts approximate, and at 

 last are united and proceed as one fibre. I am 

 doubtful if this can be considered as a tendinous 

 point of union of all three. These points of 

 union are often arranged in one line so as to 

 give some appearance of a pennated muscle, 

 but the tendinous points, if they exist, do not 

 adhere to form membranes or strings. This 

 bifurcation is very evident in the connection 

 of the septal with the peripheral walls of the 



heart."t 



The auricles are formed by two sets of fibres, 

 a superficial and a deep. The arrangement of 

 these two sets of fibres does not follow the 

 same laws as those of the ventricles. The su- 

 perficial layer (fig. 276, a a, fig. 277, a a), 

 surrounds the base of the auricles, and is of 

 unequal height and thickness. It is broader 

 on the anterior and narrow on the posterior 

 surface, more particularly on the posterior and 

 outer part of the right. It extends upwards 

 towards their superior edge on the anterior 

 surface, and on the posterior surface of the 

 left as far as the inferior pulmonary veins. 

 It is very thin, particularly on the outer 

 and posterior part of the right auricle. In its 

 course round the auricles the fibres diverge to 

 enclose the appendices, and the orifices of the 



* Dr. Duncan has given a very minute descrip- 

 tion of the fibres of this and other parts of the 

 heart, which are much too long for insertion here. 

 He has also given a very accurate and minute de- 

 scription of the bone in the heart of the ox. 



t Dr. Duncan- 



2 tt 



