916 



THE ORGANS OF VOICE 



tin- inferior thyn.id artery, and in the lower part of its extent it is united to its 

 fellow of the oi)i)osite side l>y the isthnnis. 



Relations of the Isthmus. — The isthmus varies in )»readth from a quarter to 

 three-quarters of an inch (6 to 18 nmi. ). Its anterior surface is convex and it lies 

 in relati«Mi with the dee}) fascia, anterior jugular veins, superficial fascia and skin. 

 Its posterior concave surface rests upon the second, third, and fourth rings of the 

 trachea. Its extremities are connected with the lower parts of the inner borders of 

 the lateral lobes. Its lower border gives exit to some trilnitaries of the inferior 

 thyroid veins and its upper border is in relation with the anastomosis between the 



Fui. ry'M. — View of Thvkuid Body. 



SMALLER CORNU OF HVOID BONE 



Thyro-hyoid ligament 



THYROID CARTILAGE 



THYROID ISTHMUS 



BODY OF HYOID BONE 



Thyro-hyoid membrane 



Thyro-hyoid muscle 

 Inferior constrictor 



Sterno-thyroid muscle 



Median portion of crico- 

 thyroid membrane 



Crieo-thyroid muscle 



LATERAL LOBE OF THYROID BODY 



SECTION THROUGH CARTILAGES 



internal terminal ])ranches of the superior thyroid arteries, frequently a pyramidal 

 ])rocess springs from it, and the levator glandulse thyroidea, if present, is attached 

 to it. 



The pyramidal process is variable; when present it is attached l)y its base to 

 the upper border of the istlimus or to the adjacent part of the left lateral lobe. It 

 is the remains of a duct, tlie thyro-glossal duct, which extends in the foetus from 

 the foramen cfccum of tlie tongue, l)eliind the hyoid l)one, to the isthmus of the 

 thyroid l)ody, wliicli is developccl from its lower extremity. 



The capsule and suspensory ligaments. — A ti])rous capsule of deep cervical 

 fascia completely encloses the thyroid body and sends septa inwards between its 



