370 HISTOLOGY OF THE MORBID PROCESSES. 



FIG. 334. 



Melanosarcoma of the skin. (Ribbert.) The growth is an alveolar large round-cell sarcoma, 

 containing cells that have undergone a pigmentary degeneration. Some of these cells 

 contain so much pigment that the cellular constituents are invisible. 



considered as rather more malignant than the non-pigmented forms 

 of those tumors (Fig. 334). 



II. THE MUSCULAR TUMORS. 



Muscular fibres of either the smooth involuntary or the striated 

 variety may enter into the formation of tumors. Tumors made up 

 of the former are called leiomyomata; those containing striated 

 muscle, rhabdomyomata. 



1. Leiomyoma. The cells of the tissue forming leiomyomata very 

 closely resemble those of normal smooth muscular tissue, but they 

 may show a greater variation in size. They are arranged in bundles, 

 their long axes parallel to each other ; and these bundles are inter- 

 woven in such a way that sections of the tumor contain longitudinal, 

 oblique, and cross-sections of the individual fibres (Fig. 335). Between 

 the bundles there is a variable amount of fibrous tissue, giving sup- 

 port to the bloodvessels of the tumor. This fibrous tissue may be 

 so abundant as to form a large element in the structure of the tumor, 

 which is then denominated a fibromyoma. It may, also, occasion- 

 ally be imperfectly developed, converting the growth into a leio- 

 myosarcoma. The muscular tissue may undergo a hyaline degen- 

 eration and become the seat of calcareous infiltration, or the cells 

 may be the seat of fatty degeneration with subsequent softening. 



Leiomyomata arise in parts which normally contain smooth mus- 



