TUMORS. 



309 



made up principally uf round cells and in those that have a lim- 

 ited amount of intercellular substance. The vessel walls may 

 be normal or they may be composed of sarcomatous tissue. De- 

 generate or necrotic chang-es in the tissue necessarily alter the 

 microscopic appearance. 



Fig:. 164. — Section of a mixed cell Sarooma of tlir inferior maxilla of a h(irs<\ 



These tumors are usualU- diffuse; that is, the^' are ncit encap- 

 sulated. They form metastases, and hence are malignant. 



Alveolar Sarcoma. — This is a sarcoma characterized b\' the 

 arrangement of the sarcoma cells into groups or nests, and is 

 occasionally found on domestic animals, especialh- in the ox and 

 hog. The reproductive glands, ovary and testicle, are the struc- 

 tures most frequently invaded by them. They may become 

 quite large. An alveolar sarcoma obtained from the ovary of a 

 heifer weighed l.'J kilograms (oH lbs.) and was about 20 cm. (8 

 in.) in diameter. 



Microscopically the cells are usually round, although they 

 ■may be spindle-shaped. The stroma of the tumor is made up of 



