MUSCULAR FIBRE-CELLS. 



389 



On the other hand, the new-formation of 

 fibres is going on during the first half of preg- 

 nancy; when fibre-cells in all stages of deve- 

 lopment occur in great numbers. Fig. 244, a, re- 

 presents the appearance of these during the 

 sixth month. It appears that no new develop- 

 ment of fibres occurs after the sixth month is 

 completed; subsequently to that period, Kolliker 

 could find only the colossal fibres, already de- 

 scribed. (Fig. 244.) 



After parturition, the uterus is diminished in 

 respect to all its histological elements. But of 

 its muscular fibres some are doubtless com- 

 pletely resorbed; while others become atro- 

 phied. Indeed, in three weeks after parturi- 

 tion, the fibres are found to be as short as in the 

 virgin uterus. Fat-drops also appear in them; 

 and this change can only be regarded as essen- 

 tially a fatty degeneration, to a certain extent, 

 of the fibre-cells. Their appearance at this pe- 

 riod is seen in Fig. 248. 



Fig. 248. 



Smooth muscular fi- 

 bres from the uterus 

 three weeks after partu- 

 rition, showing fat-drops 

 in their interior. The 

 four cells at the left have 

 been treated with acetic 

 acid. (KMiker.) 



Distribution of Muscular Fibre- Cells in the Lower Animals. 



It is a singular fact that the smooth muscular fibre is not found 

 at all in the Invertebrata ; the 'fibres thought to be such, actually 

 being allied genetically to the striated muscular fibres of the higher 

 animals. (Kolliker.) The following peculiarities occur in the Yer- 

 tebrata: fiffJY-- 11 



1. In the mammalia, except man, these fibres form the genito- 

 rectal muscle. In the orang-outang they are found upon the hair- 

 sacs, as in man. They also occur in the spleen of many mamma- 

 lia (p. 388, 9). 



2. In birds, smooth muscular fibres exist in the skin, forming the 

 muscles of the quill-feather; the latter having tendons of elastic 

 tissue. In the gizzard of birds they are of a bright red color, and 

 are united with a tendinous membrane. 



3. In the amphibia, they exist in the iris. Also in the frog, they 

 are found in the lungs. 



4. In fishes, they are found in the swimming bladder. In the 

 plagiostomata they occur in the mesentery, and in the osseous 

 fishes in the campanula Halleri. 



