206 



THE THYKOID BODY. 



Commonly this process lies somewhat to the left ; occasionally it is 

 thicker above than below, or is completely detached, or is split into 

 two parts : sometimes it appears to consist of fibrous tissue only. 

 In many cases muscular fasciculi, most frequently derived from the 

 thyro-hyoid muscle, but occasionally independent, descend from the 



Fig. 190. Fig. 199.— Magnified View of 



SEVERAii Vesicles from the 

 Thyroid Gland of a Child (from 

 Kolliker). 



<7, connective tissue between the 

 vesicles ; h, capsule of the vesicles ; 

 . c, their epithelial lining. 



hyoid bone to the thyroid 

 piand or its pyramidal process. 

 They are known as the levator 

 (/landnlce thi/roidem (fig. 198, 

 //). It sometimes, though 

 rarely, happens that the 

 isthmus is altogether wanting 

 the lateral lobes being then 

 connected by areolar or fibrous 

 tissue only : this is the natural 

 condition in some animals. 

 Each lateral lohe, measures 

 usually two inches or upwards in length, an inch and a quarter in 

 breadth, and three-quarters of an inch in thickness at its largest 

 part, which is below its middle : the right lobe is usually a few lines 

 longer and wider than the left. 



The isthmus measures nearly half an inch in breadth, and from a 

 quarter to three-quarters of an inch in depth. 



The ivcight of the thyroid body varies ordinarily from one to two 

 ounces. It is always larger in females than in males, and appears 

 in many of the former to undergo a periodical increase about the time 

 of menstruation. It commonly varies a good deal in size, and occasion- 

 ally undergoes enormous enlargement, constituting the disease called 

 goitre, or bronchocele. Its colour is usually of a dusky brownish I'ed, 

 but sometimes of a yellowish hue. T\\q function of the thyroid body is 

 unknown. 



Structure. — The texture of this organ is firm, and to the naked eye 

 appears coarsely gi-anulai*. It is invested by a thin transparent layer 

 of dense areolar tissue, which connects it with the adjacent parts, sur- 

 rounds and supports the vessels as they enter it and imperfectly 

 separates its substance into small masses of irregular form and size. 

 This interstitial areolar tissue is free from fat, and contains elastic 

 fibres. 



When the organ is cut into, a yellow glairy fluid escapes from 

 the cut surface. Its substance is composed of multitudes of closed 

 vesicles, which are surrounded by capillary vessels, and arc held together 

 in groups or imperfect lobules by areolar tissue. The size of the vesicles 

 varies from -frl-^^th of an inch to that of a millet-seed, so as to be visible 

 to the naked eye, — varying, however, in different individuals, more than 

 in the same thyroid body. They are spherical, ovoid, or flattened, and 



