290 CLINICAL APPLIED ANATOMY. 



ligaments of the gland, and when it is enlarged may appear as 

 strong supporting cords. The recurrent laryngeal nerves lie in 

 close contact with the outer or posterior surf aces of these ligaments. 

 The arrangement of the capsule on the posterior aspect of the 

 gland is important. As the fibrous coating is traced from the 

 convex surface of each lateral lobe backwards it will be found to 

 split into two layers, one of which remains in close contact with 

 the gland, completing its posterior investment, whilst the other 

 passes to the posterior surface of the pharynx and ossophagus, 

 imprisoning those tubes together with the trachea in the hollow 

 at the back of the gland. This part of the capsule, being dense 

 and firm, forms a conspicuous object during operation, and if un- 

 wittingly followed backwards under the belief that it is the imme- 

 diate posterior investment of the gland, may lead to the infliction 

 of wounds on the oesophagus or trachea which are enclosed by it. 

 Operations on the thyroid gland necessitate the opening up of 

 the planes of cervical fascia, so that is there is a liability to the 

 occurrence of cervical and mediastinal cellulitis as complications. 



Of the muscles which cover the thyroid gland, the sterno-mas- 

 toids are most superficial. When the gland is enlarged, these 

 muscles are usually displaced outwards, so that the thyroid 

 tumour appears in the interval between them. Occasionally 

 the tumour presents at the posterior border of the sterno- 

 mastoid displacing the muscle inwards. The sterno-hyoid and 

 the sterno-thyroid muscles become flattened over the enlarged 

 gland and may occupy grooves on its surface. The tension 

 exerted on the omo-hyoid which also crosses the gland on its way 

 to the hyoid bone, may cause the posterior belly of the muscle to 

 form a prominent cord-like projection across the base of the 

 posterior triangle of the neck. 



The vascular relations of the gland are important. There is a 

 rich plexus of veins immediately inside the capsule, and these it 

 is inadvisable to wound. On each side the gland is in immediate 

 relation with the carotid artery and internal jugular vein. 

 Enlargement of the gland usually tends to displace these struc- 

 tures outwards, but there is a great difference in the degree of 



