MORPHOLOGICAL-STUDIES ON THE THYROID-GLAND OF CHICKEN IN ADDITION TO SEASONAL-CHANGES

The thyroid glands of 31 chickens at the age of 17 to 24 months were i nvestigated. Different methods of anatomical preparation, casts of ves sels and scanning electron microscopy were used. The thyroid gland of birds is a paired organ. It is located on the ventral surface of the b ase of the neck within the thoracic inlet. The left thyroid gland is p laced more cranially than the right one. Each thyroid gland is closely connected to the common carotid artery on the medial side, from which it is supplied and to the jugular vein on the lateral side. It is a r eddish-brown organ and of lenticular profile. The gland measures on av erage 10 mm in length, 6 mm in width and 2 mm in thickness, and is cov ered by a thin connective tissue capsule which holds adipose cells. It seems that each thyroid follicle is surrounded by a net of capillarie s. The investigation by scanning electron microscopy proved that the f ollicles are oval with a pyramidal top on each end. The cuboidal epith elium cells leave impressions in the colloid. Epithelium cells carry m icrovilli on the follicle side surface. Described seasonal changes of the thyroid gland in size and activity were able to be confirmed by th e examination of the organ in July and December. In winter the follicu lar cells were higher and the follicles had a greater volume.