TUMORS, 



373 



striated muscle-fibres, arranged in irregular, interwoven bands, with 

 a little vascular fibrous tissue among them. In other cases the 

 muscular fibres are sparsely distributed through the growth, and 

 can often be found only after a prolonged search. In these cases 

 the tissue in which the muscle is situated is usually some variety of 

 sarcoma, when the whole tumor is known as a rhabdomyosarcoma 

 (Figs. 336, 337, and 338). Such mixed tumors are most frequently 

 found in the genito-urinary tract, especially in the kidney, and may 

 attain very large size. They are apt to occur in the early years of 



FIG. 338. 



Isolated cells from a rhabdomyoma of the heart. (Cesaris-Demel.) 



life, and are probably due to developmental anomalies. The sarcom- 

 atous element, which is usually predominant, gives them a highly 

 malignant character. 



III. THE ANGIOMATOUS TUMORS. 



Reference has already been made to the manner in which the 

 bloodvessels of a part may proliferate under the influence of the 

 inflammatory process, and also to the fact that when tumors 

 develop the bloodvessels proliferate in a similar way to form new 

 vascular areas within the tumor, from which the latter derives its 

 nourishment. These instances of proliferation may be regarded as 

 the natural response on the part of the vascular system to the de- 

 mand thrown upon it by the formation of new tissues. In a general 

 way, they are limited to the needs of the tissues which they supply. 

 A vascular proliferation may, however, take place irrespective of 



