PART THIRD. 



CONTRACTILE ELEMENTS. MUSCLE AND ITS 

 ADJUNCTS. 



I. MUSCLES IN GENERAL. 



THE muscular elements are produced by metamorphosis of 

 the globules of the embryo. By studying their formation we 

 may best understand the three types presented by the muscu- 

 lar system, the contractile cell, smooth fibre, and striated 

 fibre. We notice, at the same time, 

 that the property of changing their 

 shape (or contractility), which is char- 

 acteristic of these different kinds of 

 muscles, is only the sa*me property, 

 carried to a higher degree, which we 

 have ascertained belongs to globules 

 in general. 



When an embryonic globule is 

 slightly lengthened, and its nucleus 

 becomes more visible, etc., we have 

 the contractile cell (Fig. 16, 1 ), as it is 

 found, for instance, in the smaller ar- 

 teries. 



When the cells are united at the 

 ends in such a way as to form a vari- 

 cose fibre, with elongated nuclei in 

 different parts, and granular contents, 

 we have the smooth fibre, in which, Fig 16 -Diagram of the three 

 moreover, are found all the elements forms , of ^ contractile or 



f ^i 11 y-r\' -t /- o\ muscular element * 



of the cell (Fig. 16, 2 ). 



Finally, as the fibre straightens, and the fusion of the cells 

 becomes complete, we have the striated fibre (Fig. 16, 8 ), the 



* 1, Contractile cell. 2, Smooth muscle. 3, Striped muscle. 



