392 THE TISSUES. 



cleus. These are probably the embryonic forms of the fibre-cells. 

 ( Wedl.) Fig. 249 shows the fibres and the connective tissue inclosing 

 them, as seen in a transverse section. The submucons tissue is at 

 the same time either thickened, or infiltrated with a gelatinous sub- 

 stance. 



Hypertrophy of the smooth muscular tissue is usually attributed 

 to a previous inflammation in the part ; and Engel has shown that 

 such a connection exists. 



2. Atrophy of the smooth muscular tissue occurs as a consequence 

 of old age, and of diseases attended by emaciation. 



3. Fatty degeneration of the contents of the muscular fibre-cells is 

 their most common form of involution; 1 much fat occurring at the 

 same time in the interstitial connective tissue. This last form is 

 seen most strikingly in the intestinal canal and the urinary bladder. 

 The involution of the smooth fibres of the uterus after parturition 

 has already been explained (p. 389). 



4. Pathological new formations of smooth muscular fibre very rareh r 

 occur. Their new formation in the uterus during pregnancy (p. 389) 

 must be regarded as a physiological change. 



II. STRIATED MUSCULAR TISSUE. 



It is of this tissue mainly that the muscles proper are formed; 

 and its histological and its physiological relations are of the highest 

 importance. 



This form of contractile tissue consists of fibres marked with 

 transverse stria3. (Fig. 250.) The length of the fibres varies ex- 

 ceedingly, they sometimes extending through the whole length of 

 the fleshy part of a muscle. Their diameter varies from -^-5 * 

 4^ of an inch; the average being about e j^ of an inch. They 

 are larger on the trunk and the extremities than on the head ; but 

 their size is the same in the two sexes, though the contrary has 

 sometimes been asserted. They are about one-third as large in the 

 foetus as in th*e adult. "When packed together in fasciculi, they 

 assume the form of round polygonal prisms, as seen in a transverse 

 section, in Fig. 263 ; when isolated, they approach to the cylindrical 

 form. The striaB are, on an average, about -j^ J^TF of an inch apart. 

 Yarious hypotheses have been resorted to, to account for them; but 

 it is believed, with Kolliker, that "it is still doubtful to what the 

 striation is due," though it is clearly a physical and not a vital phe- 



1 This term is used to denote a pathological change or descending metamorphosis, 

 in the histological elements of a tissue or organ. It is, however, also applied to the 

 atrophj undergone by the uterus immediately after parturition. 



