772 DR PETTIGREW ON THE RELATIONS, STRUCTURE, AND FUNCTION, 



size being placed posteriorly, and a little lower than the anterior segment. 

 The remaining segment, which is the lowest, is directed towards the septum. 

 They are flexible, more or less opaque, very strong, and somewhat crescentic 

 in shape (Plate XXVIII. figs. 19 and 20). In structure, the semilunar valves 

 are intermediate between the venous and auriculo-ventricular ones. They 

 consist of a reduplication of the fine membrane lining the vessel, strengthened 

 by certain tendinous bands, and, as was first satisfactorily demonstrated by Mr 

 W. S. Savory, of a considerable quantity of yellow elastic tissue.* Some of the 

 older anatomists, among whom maybe mentioned Lancisci,! Senac,^ Morgagni,§ 

 WiNSLOW, II and Cooper,^ believed that they had detected the presence of car- 

 neous or muscular fibres ; but Haller,** and many since his time, have gravely 

 doubted the accuracy of their observations. Very recently, Mr MooREff has 

 figured two sets of muscular fibres, which he has termed according to their 

 supposed action, dilators and retractors; and Dr MonneretJI has described 

 two similar sets, which, for like reasons, he has named elevators and de- 

 pressors. I have sought in vain for the muscular fibres in question, and am 

 inclined to think that when found, they have been mistaken for the tendi- 

 nous bands accidentally stained with blood. The tendinous bands have hitherto 

 been regarded as following three principal directions, — one band being said to 

 occupy the free margin, and to be divided into two equal parts by the nodulus or 

 Corpus Arantii, otherwise called Corpusculum Morgagni, and Corpus sesamoideum ; 

 a second band, proceeding from points a little above the middle of the segment, 

 and curving in an upward direction towards the Corpus Arantii ; the third band, 

 which is the thickest, surrounding the attached border of the segment. A careful 

 examination of a large number of mammalian hearts, particularly those of man, 

 has induced me to assign to the semilunar valves a more intricate structure. In 

 a healthy human semilunar valve§§ taken from the pulmonary artery, the follow- 

 ing seems to be the arrangement. Proceeding from the attached extremities of 

 the segment above (Plate XXVIII. fig. 19 J, fig. 20 x, and fig. 29 a), and running 

 along its free margin, is a delicate tendinous band, which gives oflP still more delicate 



* PuRKiNGE and Raeuschel liad detected elastic tissue in the Corpora Arantii, but knew nothing 

 of its existence throughout the other portions of the valves. Of its presence I have frequently satis- 

 fied myself. 



•[• De motu Cordis. 



J Traite de la Structure de Coeur, livre i. 



§ Adversaria Anatomica Omnia. 



II Exposition Anat. de la Structure du Corps Humain, p. 592 



^ Myotoniia Reformata. 



** Elementa Physiologise. Liber iv. sect. 10. 



tt Med. Gazette, March 8, 1850. 



+ + Lancet, Dec. 29, 1850. 



§§ It is very difficult to get a perfectly healthy human semilunar valve, especially if the patient 

 is at all advanced in years. Out of twenty adult hearts examined by me, nearly a half of that num- 

 ber had the valves abnormally thickened. 



