488 THE THYROID GLAND. 



proof that it performs any secretion : for although several 

 respectable anatomists haVe supposed that they discovered 

 excretory ducts passing to the windpipe, larynx, or tongue, it 

 is now generally agreed that such excretory ducts are not to be 

 found. Several instances, have, however, occurred, in which 

 air has been forced, by violent straining, from the windpipe into 

 the substance of this gland. 



[There are two membranous expansions in the neck which 

 should be noticed in its dissection. The first, called Fascia 

 Superficialis, lies immediately beneath the skin, may be 

 considered as a continuation of the fascia superficialis abdomi- 

 nis, and is strongly connected to the base of the lower jaw, 

 being also spread over the parotid gland. It is not very 

 distinct in all subjects. The second is called the Fascia Pro- 

 funda Cervicis ; it extends from the larynx and thyroid gland 

 to the upper part of the sternum and first ribs ; the great ves- 

 sels, &,c. of the superior mediastinum are placed immediately 

 below it.] 



The thyroid gland, gets a thin capsular investment, from two 

 layers of the deep-seated cervical fascicf, (fascia profunda cer- 

 mcis) as seen in fig. 125. 



The same fascia likewise gives off layers, that form cellular 

 investments or tunics to the trachea, oesophagus, and to the 

 blood-vessels of the neck. Other processes pass off from it 

 which supply sheaths to the sterno-cleido mastoid and other 

 muscles of the neck. Between the sheaths of the different 

 muscles of the neck, dense processes of cellular tissue are con- 

 tinued, so as to give them all the appearance of being formed 

 as it were, from a common fascia. At the posterior part of the 

 neck they are thus indirectly connected with the ligamentum 

 nuchce. Though this for practical purposes is not considered 

 the best way for studying the fascia of the neck, it serves to give 

 an idea of the continuity of the cellular investments, which is so 

 common throughout the body. The accompanying cut and 

 explanation is taken from Wilson. 



The two lobes of the thyroid gland, when extended and 

 measured from side to side are together about three inches in 



