I790 



HUMAN ANATOMY. 



Epiglottis 



antero-external surfaces of the lateral lobes. The isthmus varies much in size, 

 and is often more or less incorporated in one of the lobes. In lo per cent, it is 

 absent.' An upward projection, \}a^ pyraynidal process, rising from either the isthmus 

 or one of the lateral lobes, and usually regarded as a remnant of the median anlage 

 of the thyroid, is found more or less developed in probably half the cases. A typical 

 one reaches the hyoid bone, to the body of which the process is generally attached 

 either by muscle or ligament. It is rarely quite median, being more frequently found 

 on the left. Statements as to its frequency vary greatly. Streckeisen ' says it is 



wholly wanting in only about 

 Fig. 1510. . 20 per cent. ; but, since goitre 



is common in Switzerland, his 

 sources of information are not 

 of the best. Zuckerkandl, 

 however, puts the occurrence 

 of the process at 74 per cent. 

 Gruber, in Russia, found it in 

 only 40 per cent., and Mar- 

 shall, in England, in 43 per 

 cent. We incline to believe 

 that these latter figures rep- 

 resent the more common pro- 

 portion. 



The thyroid lies beneath 

 the group of infrahyoid mus- 

 cles, from which it is separated 

 by the middle layer of the 

 cervical fascia. The sterno- 

 mastoid muscle crosses the 

 lower part of the lateral lobes. 

 The inner surface lies against 

 the trachea, the cricoid carti- 

 lage, and the lower posterior 

 part of the wings of the thy- 

 roid cartilage. It reaches back 

 to the oesophagus, which it 

 touches on the left, and some- 

 times on the right also. It 

 may touch the Ibwer part of 

 the pharynx on both sides. 

 The sheath of the carotid lies 

 against the posterior surface at 

 its outer border and is in part 

 external to the organ. The 

 common carotid is usually be- 

 hind the thyroid and the inter- 

 nal jugular vein beyond it. 

 This explains how an enlarged 

 gland insinuates itself between 

 carotid is external rather than 

 to it. Internal to the carotid 

 The inferior thyroid arteries 



Superior cornu of 

 thyroid cartilage 



Occasional foramen 



Thyroid cartilage 



Crico-thyroid 

 membraue 



Cnco-thyroid 



muscle 

 Cricoid 



cartilage 

 Suspensory 



ligament 

 Pyramidal 



process 



Isthmus 



Lobule 



Trachea 



Thyroid body in situ ; anterior aspect. 



these vessels. Frozen sections show that often the 

 posterior to the organ, but still in close relation 

 sheath, it rests behind against the prevertebral fascia. 

 enter the lateral lobes from the inner side and the superior thyroid arteries from the 

 antero-external. The middle cervical sympathetic ganglion is behind. The inferior 

 laryngeal nerves lie at its inner surface, the left one being in actual contact with the 

 thyroid and the right one at least very close to it. The sheath connects the thyroid 

 body very closely to neighboring parts. It is so firmly bound to the trachea as to 

 follow its movements. Median bands to the cricoid and thyroid cartilages have been 



' Marshall : Journal of Anatomy and Physiology, vol. xxix., 1895. 

 " Virchow's Archiv, Bd. ciii., 1886. 



