560 



THE DUCTLESS GLANDS ENDOCRIN GLANDS 



of the interfollicular stroma. Colloid material, similar to that within the 

 follicles, has been repeatedly found within the lymphatic vessels (Baber, 

 Langendorf, Hiirthle) and may be readily demonstrated in most sections 



, of the thyroid. Un- 



doubtedly this does 

 not, however, repre- 

 sent the entire 'inter- 

 nal secretion' of the 

 gland. 



Blood Supply. 

 The arteries form a 

 rich plexus in and 

 about the capsule of 

 the thyroid, from 

 y which numerous 

 branches penetrate the 

 organ, lying in the 

 connective tissue trab- 

 eculse between the lo- 

 bules; they are dis- 

 tributed to all parts 

 of the gland. They 

 supply a rich capillary 

 FIG. 484. DIAGRAM OF PHARYNX OP HUMAN EMBRYO, plexus in the walls of 

 SHOWING THE ORIGINS OF THE ANLAGES OF THE the follicles. The 

 THYMUS, THYROID AND PARATHYROIDS (EPITHELIAL 

 BODIES). 



Thy 1 , earliest position of thyroid anlage; Thy 2 , sec- 

 ondary position of thyroid anlage; Tgd, thyroglossal 

 duct; Fc, foramen cecum; LThy, lateral thyroid an- 

 lages; Ptky, parathyroid bodies; pb, postbranchial 

 body; T, tonsil; /, II, III, IV, V, pharyngeal pouches; 

 a, 6, first and second branchial grooves ('gill clefts'); 

 1, 2, 3, first, second and third aortic arches in the 

 cores of the branchial arches. The complete wall of 

 the pharynx is only shown at the right, above. (Adapt- 

 ed from Kohn.) 



veins retrace the 

 course of the arteries. 

 The walls of the 

 smaller venules consist 

 only of endothelium, 

 with a very thin coat 

 of fibro-elastic connec- 

 tive tissue. 



Lymphatics. The 



thyroid is very abun- 

 dantly supplied with lymphatic vessels. These form a plexus of 

 very broad lacunar capillaries in the interfollicular connective tissue, 

 where they stand in intimate relation with the follicular epithelium. 

 From this plexus vessels pass to the interlobular connective tissue, in 

 which they form a second plexus, whence lymphatic vessels pass out of 



