STRIATED MUSCULAR FIBRE. 405 



sues after death, and which may be mistaken for the rigor mortis. 

 This, however, is in a few hours succeeded by a state of relaxation 

 of the muscles, and then the ordinary rigor mortis supervenes. 



A knowledge of all the facts connected with this subject is essen- 

 tial in certain judicial investigations; in regard to which the works 

 on medical jurisprudence may be consulted. Its cause is not under- 

 stood. It does not, however, depend upon the diminished tempera- 

 ture of the dead body, since it often occurs while the latter is still 

 warm ; nor is it produced by the coagulation of the blood, though in 

 those cases of death in which the blood does not coagulate (p. 94, vi.), 

 the rigidity usually manifests itself least. We can hardly say more 

 than that the rigor mortis is the last vital act of the muscles, as the 

 coagulation of the blood is of the fibrine (p. 93, III.). 



It should be here added, however, that the rigor mortis is equally, 

 if not more remarkable in the smooth muscular fibre. The arte- 

 ries contract so as to force their blood into the venous system; which 

 almost invariably occurs a few hours after death. They then en- 

 large as the rigidity passes off, and become quite flaccid. Hence 

 the old physiologists believed that the arteries naturally contained 

 not blood, but air, and named them accordingly. 1 The alimentary 

 canal, the bladder, and the bronchial tubes are also, for a time after 

 death, contracted in a similar manner ; and the post-mortem con- 

 traction of the parturient uterus in patients who had died unde- 

 livered, has been known in several instances to expel the foetus. 



The " concentric hypertrophy" of the heart, as it was formerly 

 called (this organ being thicker than usual and smaller), has been 

 shown by Mr. Paget to be merely the state of cadaveric rigidity 

 which usually occurs in that organ. The ventricles become rigid 

 and contracted within an hour or two after death ; and usually re- 

 main in that state for ten or twelve hours (sometimes twenty-four 

 or thirty-six even), when they again relax and become flaccid. 



Of the lower animals the rigor mortis occurs most rapidly in those 

 possessing the greatest muscular irritability (e. g. in birds), and vice 

 versa slowest, therefore, in reptiles and fishes. 



Pathological Conditions and New Formations of Striated Muscular 



Fibre. 



1. Hypertrophy scarcely occurs except in case of the tongue, heart, 

 and certain respiratory muscles ; though the increased development 



1 From a.*?, air, and rfiftca, to keep or hold an air-holder. 



