THE THYREOID GLAND 



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about 2 cm. in width, and from 1.5 to 2.5 cm. in thickness. The right is usually a 

 little longer than the left. The isthmus averages from .6 to .8 cm. in thickness 

 and from .5 to 1.5 cm. in height. 



The weight of the normal gland averages about 30 grams; but many specimens are found as 

 lightfas 20 grams, and others weigh as much as 60 grams. 



When hyperemic or congested the size of the gland may be markedly augumented. This 

 occurs normally in most women at puberty and during menstruation and pregnancy. In 

 various abnormal conditions of the gland there is an increase in size, sometimes to a marked 

 degree. These enlargements are ordinarily grouped under the term struma or goitre, and may 

 be associated with either a hyper- or hyposecretion of the gland. Decrease in size is common in 

 old age and may appear prematurely in certain diseases. 



The shape of the gland as viewed from the ventral surface is that of a capital 

 U with the concavity directed cephalically (fig. 1068). The sides of the U are 

 formed of the more or less elongated lobes connected slightly cephalic to their 



Fig. 1068. 



Lesser cornu of hyoid bone 



Hyo-thyreoid ligament 



-Ventral View of the Thyreoid Gland. 



Body of hyoid bone 



Hyo-thyreoid membrane 



Thyreoid cartilage 



Sterno-thyreoid muscle 



Thyreoid isthmus 



Median portion of crico- 

 thyreoid membrane 



Crico-thyreoid muscle 



Lateral lobe of thyreoid gland 



thickened caudal ends by the thin transverse isthmus. In transverse sections 

 through the isthmus the gland is also U-shaped with the concavity directed dor- 

 sally, the lobes being on each side and the isthmus ventral to the trachea (fig. 

 1068). The surface of the gland is somewhat unevenly roughened. 



The isthmus glandulae thyreoidae usually becomes wider laterally where it is 

 attached by its two extremities to the lateral lobes (figs. 1068, 1069). Its ventral 

 surface which is flat or somewhat convex is covered superficially by the sub- 

 cutaneous tela and skin and beneath these by the superficial and middle layers of 

 the cervical fascia. Between the layers of cervical fascia and close to the median 

 line is the sterno-hyoid muscle and more laterally and deeper the sterno-thyreoid 

 muscle. The dorsal surface is concave and is in relation with the first two to four 

 rings of the trachea and sometimes with the cricoid cartilage. 



The size and form of the isthmus is subject to considerable variation. It may be very short. 

 Rarely it is wanting entirely or connects with but one lateral lobe. Its superior border is, as a 

 rule, concave and is connected in many cases with the pyramidal lobe. The caudal border, 

 although usually on the third ring of the trachea and 2.5 to 3 cm. from the jugular notch of the 

 sternum, may be especially developed so that it extends caudally beyond the lateral lobes and 

 produces a process which is known as the medial lobe. 



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