THE MUSCULAR SYSTEM. 253 



antagonists are paralyzed, becomes intelligible. With respect to the 

 cadaveric rigidity, the important facts have quite recently come to light, 

 that it may be arrested by the injection of blood (Brown-Se'quard); and 

 also that it takes place even in the living animal, when the supply of 

 blood to a group of muscles is entirely cut off (Stannius). In the latter 

 case, the irritability of the nerves ceases at the same time, and on the 

 restoration of the circulation the normal conditions in both muscles and 

 nerves are also restored. By these facts, all hypotheses respecting the 

 occurrence of the cadaveric rigidity, except that of Weber, are contra- 

 dicted; even that of Briicke, which asserts that it is caused by the 

 coagulation of the fibrin existing in the muscular fibre. But at the 

 same time the question also arises, as to what is the proximate cause of 

 the change in the elastic conditions of the muscles, whether it be due 

 to the death or cessation of activity of the nerves, or to the deficient 

 supply of blood to the muscles themselves ? Stannius decides in favor 

 of the former supposition, and is consequently driven to the conclusion, 

 that during life the motor nerves act upon the muscles, by reducing, 

 during the state of repose, their natural amount of elasticity, whilst in 

 the contraction of the muscle the influence of the nerves is momentarily 

 relaxed. Thus, according to Stannius, the rigidity connected with con- 

 traction, and vital contraction, would be identical, and nothing more 

 than the condition of the muscle when freed from all nervous influence, 

 and lasting until the nerve again puts the muscle into a state of rest, 

 or its substance is decomposed. I must own that in this view, which 

 moreover had already been proposed by Engel (" Zeitsch. der Wiener," 

 Aerzte, 1849), I do not at present agree ; and in particular would 

 remark, that the circumstance of the contractions which occur during 

 life being much more considerable than those which attend the rigor 

 mortis, appears to be opposed to it. 



86. Development of the Muscles and Tendons. The rudiments of 

 the muscles consist, originally, of the same formative cells as those of 

 which the rest of the body of the embryo is constituted ; and it is not 

 till afterwards that the muscles, tendons, &c., are gradually developed 

 by a histological differentiation. In man, the muscles are not evident 

 before the end of the second month ; at first, however, they cannot be 

 detected by the unaided eye ; they are soft, pale, gelatinous, and not 

 to be distinguished from their tendons. In the tenth and twelfth week 

 they are more distinct, especially in specimens preserved in alcohol ; 

 and at this time the tendons also may be distinguished as somewhat 

 clearer, but at the same time transparent streaks. 



In the fourth month, both the muscles and tendons are still more 

 distinct, the former being, on the trunk, of a light reddish color, the 

 latter less transparent, and grayish, both retaining a soft consistence. 



