THE THYREOID GLAND 409 



curative. The second theory holds that the abdominal 

 sympathetic is at fault, and that the occurrence of the disease, 

 along with pathological conditions of the gland, is due to the 

 formation of adhesions with, and consequent irritation of, the 

 cceliac ganglia and their branches. 



The Thyreoid Gland. The thyreoid gland is, perhaps, 

 the most important of all the ductless glands, since it is the 

 most frequently affected by pathological conditions. It consists 

 of two lateral lobes connected to one another by a narrow 

 band of gland substance, termed the isthmus (Fig. 146). The 

 isthmus lies in front of the second, third and fourth rings of 

 the trachea, and, like the rest of the gland, it is enveloped in 

 a fibrous sheath, derived from the pretracheal layer of the deep 

 cervical fascia. 



The lateral lobe is pyramidal in shape. The pointed apex 

 is superior and lies in contact with the lamina of the thyreoid 

 cartilage. The enlarged base is inferior and extends downwards 

 to the level of the sixth or seventh tracheal ring. The deep 

 surface of the lateral lobe is in contact with the thyreoid and 

 cricoid cartilages and the upper six or seven rings of the 

 trachea, but it usually extends farther backwards and comes 

 into relationship with the inferior constrictor of the pharynx 

 and the oesophagus. Its lower part, therefore, is related to 

 the recurrent (laryngeal) nerve, which ascends in the groove 

 between the trachea and the oesophagus and disappears under 

 cover of the inferior constrictor (Fig. 49). 



Tumours of the Thyreoid Gland. When the thyreoid gland 

 becomes enlarged, the effects are mainly produced on the 

 deep relations. There may be difficulty in respiration owing 

 to pressure on the trachea, but, owing to the strength of the 

 tracheal walls, this symptom may be preceded by dysphagia. 

 In addition, one or both recurrent nerves may be involved, 

 and irritation of them leads to unilateral or bilateral abductor 

 paralysis (p. 338). Section of the thyreoid isthmus is sufficient 

 to do away with the respiratory embarrassment, since it removes 

 the constricting band. 



