THE HEART 



9i)0 



surfaces the chordse tendineop form an arched interlacement, which has bocn well 

 likened to tin- fan tracery of Gothic architecture. (Macalister. ) 



The left auricle is placed hehind the roots ui the aorta and pulmonary artery, 

 with the right auricle overlapping it, and lying to the right of these structures. 

 Behind, it receives on each side the pulmonary veins, and it is separated Ijy the 

 pericardium from the oesophagus and the descending thoracic aorta. Its narrow 

 and much curved appendix arches round the root of the pulmonary arter}', and is 

 the only part of the auricle to be seen from the front. The cavity of the auricle 

 is smooth, with the exception of the api^endix, in which the musculi pectinati are 

 well marker 1. 



Openings. — Besides the narrow opening which leads from the atrium into tin- 

 appendix, the left auricle presents posteriorly the orifices of the four pulmonary 

 veins, two of which sometimes have a single mouth, whilst ;i third may l)e])resent, 

 especially on the right side. The oval auriculo-ventricular opening is placed 

 below and in front. Several small orifices, the foramina Thebesii, are also to be 

 found in the cavity. A crescentic indentation on the sei>tal wall, with its con- 

 cavity upwards and placed above the level of the annulus ovalis, indicates the 

 upper border of the valve, which has grown upwards to obliterate the foramen 

 ovale, but which now is adherent and forms part of the wall dividing the two 



Fig. 552. — Vikw of the Aurtcul.vr C.avitiks from below (the Transverse Section 



PA.SSIXG above their MIDDLE). 



^^=-^.: 



^" ■ Orifice of supe- 



rior reiiii ciirii 



Musculi 

 pectiuati 



<^ V ^^ \, '■ Vf pectinat 



■ "-^fV- •' Ri'jilt auricular 

 a]>peniiii 



auricles. As already ol)served, a small obli(iue oritiee sometimes remains un- 

 closed. 



The left ventricle forms the chief jjart of the heart behind, with its ajiex and 

 left border. It is somewhat longer and narrower than the right. Its cavity is 

 conical with the apex below and it is somewhat ovoid in transverse section. Its 

 muscular wall, which is much thicker than that of the right ventricle, is thinnest 

 at the apex and thickest at the junction of the uj)per and middle thirds. 



The columnae carneae are numerous, small, and closely reticulated, giving to 

 the interior of the ventricle, especially near the apex, a cavernous appearance. 



The musculi papillares are usually represented by two large, sometimes com- 

 pound, muscular ])illars, which arise from the nnterior and the posterior wall 

 respectively; and from tliese tlie chordse tendineae pass to the edges and surfaces 

 of the two segments of the Ijicusjnd valve. 



The orifice of the aorta looks somewhat forwards, and is guarded V)y three 

 semilunar valves, which are sifnilar in structure, but present more strongly 

 marked i-haracters than are to l)e found in the corresi)onding valves of the pulmo- 

 nary artery. One of these segments is placed anteriorly and two lie posteriorly. 

 It is surrounded by a fil)rous ring, similar to that which strengtliens the i»ulmonary 

 orifice, and the walls of that ])ortion of the cavity which lies immediately below it, 

 the aortic vestibule, are entirely fibrous. 



