1878.] 



of the Thyroid Gland. 



59 



cylinder, next to the capillaries, being arranged at right angles to the 

 long axis of those vessels. Each cell is provided with a nucleus, 

 usually oval in shape. In very few, if in any, of these cylinders have I 

 been able to detect any central canal. In the dog I have always 

 observed these "undeveloped portions" as distinct bodies, not con- 

 tinuous with the normal gland tissue, but separated from it by 

 layers of connective tissue, and frequently lying in depressions on 

 the surface of the gland. They appear to be portions of gland, whose 

 development has become arrested at an early stage, and there is no evi- 

 dence to show that they undergo any further development subsequently. 



In the kitten similar undeveloped portions are seen, but in this 

 animal they may sometimes be observed to be continuous with the 

 ordinary gland tissue. In this case a formation of vesicles from the 

 cylinders of cells appears to be taking place by the growth into them 

 laterally of processes of connective tissue with blood vessels, and by 

 their excavation into vesicles. In the kitten the cylinders are less 

 convoluted than in the dog, and throughout the gland the fully formed 

 vesicles frequently appear grouped in rows, which have a more or less 

 parallel arrangement. Somewhat similar, but shorter, cylinders of 

 cells are seen in the thyroid of the pigeon, scattered throughout the 

 gland . I may mention that in the thyroid glands of foetal pigs 

 (measuring about 2\ inches in length) before the formation of vesicles 

 has taken place, I have seen cylinders presenting an appearance 

 similar to those above described. 



In sections of the glands of young dogs (aged about five weeks and 

 three months respectively) I have observed that the vesicles are very 

 much branched, and present numerous hollow ramifications. In the 

 thyroid glands of numerous other dogs of different ages, I have with 

 equal certainty ascertained that the vesicles presented very few, if any, 

 of these hollow branches. These much- branched vesicles are doubt- 

 less the hollow branched cavities (tubes) of Zeiss, which he obtains by 

 floating them out from portions of the fresh gland of young animals. 

 In glands in which the vesicles present this appearance, the walls of the 

 vesicles are frequently infiexed so as to form numerous projections into 

 the interior, as already described by Yerson and myself. Zeiss has 

 repeatedly endeavoured to inject these hollow-branched cavities by the 

 method of puncture, but without success. Neither have I, in all my 

 injections, ever succeeded in filling any such structures, which must 

 surely have been the case if the hollow-branched cavities were in com- 

 munication with one another to any extent, for it seems almost impos- 

 sible to suppose, as Zeiss does, that the contents of these cavities 

 can prevent the injection from running into them, whilst we know that 

 the viscid contents of the lymphatics have no such effect. I am of 

 opinion that these hollow branched cavities do not communicate with 

 one another to any extent, and that, in the dog at least, they merely 



