To these are added other varieties mentioned below.

Fig. 77

Osteoma of frontal sinus. (Neisser.)

Fig. 78

Recurring sarcoma of parotid. (Original.)

A. Round-cell Sarcoma.

—This is simple in construction, and consists of round cells containing very little intercellular substance. The nuclei of the tumor cells stain easily, the cells themselves varying in size in different cases. Bloodvessels lead up to the tumor, but in the interior appear rather as channels. These tumors have no lymphatics: they grow rapidly, infiltrate easily, recur quickly, and give rise to numerous metastatic or secondary deposits. They may affect any part of the human body. The size of the cells is supposed to be in some measure an index of their malignancy—the smaller the cell the more malignant the tumor. They appear at all periods of life. They are perhaps the most commonly seen of malignant tumors in animals. (See [Plate XVII].)