xiv EXI'LANATION OF THE PLATES. 



fawicnlated, and running a straigliter course than in the 

 substance of tlie organ. 



Fig. 12. A portion of the thyroid from a human foetus, slightly com- 

 pressed. It exhibits the same structure as the thymus, but 

 its fibrous toxture is }n()re developed. 



Fig. 13. A portion of the same thyroid to show its vascular network, in 

 the meshes of which, as in Fig. 12, the cells are seen arranged 

 in gi'oups. 



CENTRES OF NUTRITION.— Plate IV. page 389. 



Fig. 1. A portion of the middle and internal meml)ranes of a large 

 encysted tumour situated under the tongue, and removed by 

 Professor Synie. 

 a. The middle or second membrane, which is a germinal 

 membrane, consisting of flattened cells, the lines of junction 

 of which are faintly visible, the nuclei remaining as the 

 germinal spots of the membrane. 

 I. The internal meml)rane, a layer of small cells, somewhat 

 spherical, with slightly granular contents. 



The external membrane of the cyst, consisting of areolar 

 and elastic fibres, contained the blood-vessels of the morbid 

 growth. 



The cyst contained a soft mass resembling thick honey 

 in consistence. The outer layer of this mass was white, and 

 consisted of large, flat, transparent cells or scales, with few or 

 no traces of nuclei. The larger internal part of the mass 

 was reddish-grey, and consisted of ovoidal cells, resembling 

 those of the external layer, except that they were turgid 

 with a transparent oily-like fluid, and contained nuclei in 

 various stages of development. 



Fig. 2, a. Fig. 3, a. Cells of the meliceritous mass — those without 

 nuclei being those of the white external layer, the others 

 belonging to the reddish-grey part of the mass, presenting 

 nuclei in various stages of development. 

 h h. Some of the latter cells, in which the nuclei have become so 

 much developed as to distend their cells beyond the average 

 size. In these enlarged cells, it will be remarked that the 

 nuclei, instead of remaining as single germinal spots for each 

 cell, have broken up into numerous spots or centres of 

 nutrition. 



In a tumour of this kind, the cyst and its contents are 

 two distinct parts, and perform two distinct actions. The 

 cyst is the active agent in withdrawing materials of nutrition 

 for itself and its contents from the vessels wliich ramify in 

 its outer tunic. The organs which accomplish this are the 

 germinal spots in its middle tunic, which, in virtue of forces 



