402 BULLETIN OF THE BUREAU OF FISHERIES. 



find total destruction of cartilage and bone and marked evidences of infiltration of the 

 bony and cartilaginous structures by individual cells and groups of cells. (Fig. 48 

 and 49.) 



Infiltration of vessel walls. — Genuine infiltration of vessel walls will serve much the 

 same purpose as infiltration of the capsule in mammals, as deposits of thyroid tissue 

 within the media of the larger vessels has never been encountered. Figures t,t, and 

 50 show a section of the aortic wall stained with orcein, in which the elastic lamella; 

 of the media are split up and spread out into the adjoining tumor mass as the result 

 of the penetration between the elastic lamellae of the alveoli of an infiltrating tumor. 

 The aortic wall at this point is reduced to about half the thickness of the uninfiltrated 

 remainder of the circumference. We have here genuine infiltration of the media of the 

 aorta. 



Infiltration of muscle. — Besides the growth of the alveoli of tumors between the 

 muscle bundles (fig. 37), we frequently encounter infiltration of individual muscles cells 

 by tumor cells. In these cases the sarcolemma sheath is broken through and we find 

 the isolated cells of the tumor displacing the muscle fiber. (Fig. 5 1 .) The tumor tissue 

 in many instances has lost its alveolar structure, the cells being closely packed together 

 without definite form. There are many instances of genuine infiltration by individuals 

 or groups of cells in the muscle fibers. 



Infiltration of the skin. — This is usually best observed in the floor of the mouth. 

 It has been suggested that the breaking through of tumor masses of the outer integu- 

 ment was due largely to pressure, that the epidermis became greatly thinned and ulti- 

 mately eroded. This is in many instances true where large masses of tumor protrude 

 into the floor of the mouth or where protuberant growths extend downward or outward. 

 In the floor of the mouth, however, we frequently find that the elastic structure of the 

 skin and the epithelial strata overlying it are punctured by small vegetations. Figures 

 31 and 32 show such growths. Frequently growths penetrating the floor of the mouth 

 will be found to have split up and destroyed the elastic structure of the epidermis without 

 any appreciable thinning whatsoever, the entire thickness of the elastic structure sud- 

 denly disintegrating without any evidence of stretching or thinning. (Fig. 46.) It 

 is therefore evident that besides expansive growth, carcinoma of the thyroid in the Sal- 

 monida: presents indisputable evidence of genuine infiltration, such as we encounter 

 in malignant growths in other species. 



OTHER OBSERVATIONS. 



In 1905, L. Pick published a comprehensive article entitled "Carcinoma of the 

 Thyroid in the Salmonidse, " with 15 illustrations. It is by all means the most important 

 publication on this subject dealing with the histology of these tumors. Pick's material 

 consisted of 10 brook trout obtained from a hatchery, we are led to believe, in the United 

 States. He illustrates five of these fish, one of which exhibited a large infiltrating 

 tumor involving the entire region below the floor of the mouth and the muscular struc- 

 ture of the isthmus (Pick, 1905, fig. i). Figure 3 shows a small tumor at the branchial 



