THE THYREOID GLAND 1317 



mainly the dorsal and lateral surfaces of the caudal part of the gland (fig. 1071). There is 

 usually a well-marked branch which passes cephalically to anastomose with a good-sized 

 branch from the superior thyreoid. Small branches are distributed to the ventral surface of the 

 caudal portion of the lobes and isthmus. The small fifth artery, the thyreoid ima artery, 

 occasionally present, ascends on the ventral surface of the trachea and reaches the gland at the 

 caudal border of the isthmus or of either lobe. It anastomoses with the other arteries which 

 may be correspondingly reduced in size. The above-mentioned arteries branch freely and are 

 distriljuted over the surface of the gland between the two layers of the capsule where they 

 anastomose extensively with one another and with the arteries of the opposite side. From the 

 surface plexus branches pass with the septa and trabeculae through the gland to break up into 

 the capillary plexuses around the vesicles. 



The relation of the inferior thyreoid artery to the recurrent nerve is important from a 

 surgical point of view but unfortunately is not constant. In some cases the nerve is ventral 

 to the artery, more often on the right, in other cases it is dorsal and often the nerve passes be- 

 tween the branches of the artery. Their relation is most intimate close to the trachea Fig. 1073. 



Fig. 1072. — Vessels of the Thyreoid Gland, Anterior View. 1, 2, 3, Lateral lobes and 

 isthmus; 4, pyramidal lobe; 5, hyoid bone; 6, thyreoid cartilage; 7, trachea; 8, common carotid; 

 9, internal jugular; 10, thyreo-linguo-facial vein; 11, superior thyreoid artery; 12, inferior laryn- 

 geal vessels; 13, middle thyreoid vein; 14, subclavian artery; 15, inferior thyreoid artery; 16, 

 inferior lateral thyreoid veins; 17, inferior medial thyreoid veins; 18, left innominate vein; 19 

 aortic arch; 20, vagus nerve. (Testut.) 



The veins (fig. 1072) issue from the substance of the gland along the septa 

 which penetrate from its capsule. Between the two layers of the capsule they 

 form a rich plexus of large vessels from which three large branches issue on each 

 side. 



The superior thyreoid veins leave the capsule of the ventral surfaces of the lateral lobes 

 near their apices and pass cephalo-laterally to empty into the internal jugular veins, sometimes 

 with the facial veins. The middle thyreoid veins are sometimes absent, when present they are 

 often very small and pass from the lateral border of the lateral lobes laterally to empty into the 

 internal jugular vein. The inferior thyreoid veins arise from the caudal and lateral part of 

 the dorsal surfaces of the lateral lobes and pass caudolaterally to open into the innominate 

 veins. Ventral to the trachea, caudal to the isthmus, the two inferior thyreoid veins are 

 connected by numerous cross anastomoses and occasionally they open by a single trunk which 

 joins the left innominate vein. A thyreoidea ima vein is sometimes present. 



The lymphatics of the thjTeoid gland begin as abundant plexuses aroimd the vesicles of the 

 gland lobules. These connect with the interlobular branches which empty into radicles 

 accompanying the blood-vessels through the septa to the surface of the gland where they 

 join a considerable plexus placed between the two layers of the capsule. From the cephalic 

 portion of the isthmus and lobes efferent vessels extend cephalo-medially to one or two small 



