414 EDGAR H. NORRIS 



Wolfler ('83) described the process of later development in 

 the human thyroid gland as centrifugal. He distinguished a 

 cortical and a medullary portion, which are respectively young- 

 est and oldest, least developed and most developed portions. 



His ('85) described in the thyroid gland of an embryo (Zw) 

 between 16.5 and 22 nrni. in length cells grouped to form acini 

 or tubes. The inner ends of the cells have a light, colloidal 

 appearance. 



Biondi ('89) found that the (postnatal) thyroid vesicle dis- 

 charges its contents, collapses and finally rearranges itself in the 

 form of a number of small acini which repeat the process. He 

 held that the colloid arises by cell secretion, and not by cell 

 degeneration. 



Ribbert ('89) described a centrifugal growth of the thyroid in 

 embryos and newborn. FoUicles are formed by the outgrowth 

 of solid buds or sprouts from the old follicles. 



Lustig ('91), who studied the thyroid gland in the pig and 

 other animals, affirmed that colloid and follicles appear syn- 

 chronously as the result of the degeneration of the central cells 

 of the preexisting solid masses. 



Podack ('92) found well formed follicles in a fetus of five 

 months. In some parts of the gland the follicular structure is 

 only suggested and many cell-masses and cell-cords are present. 



Marshall ('93) found that the thyroid in chick and frog em- 

 bryos presents a stage in which the gland is made up of com- 

 municating, epitheUal tubes. In the rabbit he described the 

 presence of out-growths, some solid and some hollow, from the 

 primitive epithelial anlage. In the human embryo: ''At an 

 early stage the lobes are excavated by a number of detached 

 cavities, which become the vesicles of the adult thyroid." 



Ziefinska ('94) found the structure of the thyroid in newborn 

 children variable both in size and number. of the follicles, and 

 also in the amount of solid cell masses. The relations "errinern 

 an acinose Driisen und erwecken den Gedanken, dass hier ein 

 sich verastelnder Driisenkanal vorliegt, als dessen Endblaschen 

 die solide Zellhaufen gelten konnen." 



