THYEEOID IN TUETLES 283 



Mammalia. Aside from the human thyreoid, the detailed de- 

 scription of which may be found in any treatise on anatomy, it 

 may be remarked that, in general, this organ in mammals con- 

 sists of two lateral lobes at the sides of the trachea, between the 

 first and the ninth tracheal rings — the exact position depending 

 on the animal; the weight and volume also vary with the animal. 



In general the two lobes are joined to each other by an isthmus, 

 usually thin, as in the dog, cat, rabbit, rat, and guinea-pig; in 

 old animals it may atrophy or disappear. Thus in the donkey 

 the isthmus is easily seen in the young animal, while in the old it 

 is reduced to a slight atrophic filament without glandular struc- 

 ture. In the horse and sheep, on the other hand, the isthmus is 

 so thin that often it cannot be distinguished; this has led some 

 to beheve that in these animals it occurs only exceptionally. 

 Aberrant nodes of thyi-eoid tissue have been described in non- 

 human mammals; in these, however, it has not been possible 

 to recognize the pyramid 'of Lalouette or the appendix of 

 Morgagni. 



PERSONAL INVESTIGATIONS 



My researches on the thyreoid of Chelonia were carried out 

 on the two Itahan species, Emys europaea and Testudo graeca. 

 There is very little difference in the macroscopic aspect and no 

 difference at all in the microscopic appearance of the thyreoid in 

 these tw^o species. I will give the description of the thyreoid of 

 Emys europaea and refer to Testudo graeca for the main differ- 

 ential points. 



Macroscopic anatomy. In Emys europaea the thyreoid is a 

 single medial organ of spheroid form and pinkish color, located 

 in the cavity of the arch formed by the truncus innominatus. 

 From the anatomic-topographic point of view, in order to reach 

 the thyreoid by trepanning it is necessary to apply the point of the 

 instrument half a centhneter above the point of union of the 

 hyoplastral with the hypoplastral plates. Removing the bone, 

 and taking pains to hold the animal's forepaws well apart so as to 

 withdraw from the operative field the two scapuloclavicular 

 ligaments (with the animal's neck extended), one finds a small 



