412 j^ose, Pharynx and its Derivatives in Man 



article. I give his exact words below because they have served as a 

 basis for our knowledge of the subject since they Avere written. 



In this series of models the thyroid rudiment appears in the earliest 

 one studied (embryo XII at the end of the 2nd week). In this embryo 

 it is represented as a rounded eminence directly on the ridges uniting 

 the first pair of visceral pouches. It is broader from side to side than 

 it is ventro-dorsally, making its outline elliptical. This is the rudiment 

 of the thyroid gland and the ductus thyreoglossus. 



In the model of the fourth week embryo (Thyr. m., Fig. 3, embryo 

 II), it is a solid structure arising from the dorsal part of the apex 

 of the angle formed by the junction of the ridges running inward 

 from the 1st pair of visceral pouches. It is just oral to the hollow 

 space representing the inner of the 2nd visceral arches. Directly oral 

 to it is a hollow space representing the tuberculum impar. The thyroid 

 rudiment consists of a slender stalk surmounted by a knob facing 

 aborally (dorsally also in this embryo). Its shape might be compared 

 to a pipe with a short stem and the bowl facing the back. The 4th 

 visceral pouch (V. P.'^, Fig. 2) is a flattened object with the part 

 attaching it to the pharynx slightly smaller than the distal end. It 

 shows no thickening or development into the lateral thyroid rudiment. 



In the next stage, as seen in embryo CLXIII, the thyreoglossal duct 

 remains as a small conical eminence on the ridge connecting the first 

 visceral pouches (see D. Th. gl., Fig. 5). It is at the junction of the 

 tuberculum impar and the two dorsal rudiments of the tongue. The 

 median thyroid rudiment has become entirely disconnected and sunken 

 to the level of the 3rd visceral fold. It has spread out laterally and 

 has a bilobed structure. The left lobe is decidedly the longer and 

 approaches closer to the floor of the mouth than the right. The 4th 

 visceral pouches (V. P.)'^, Figs. 4 and 5) appear as two ventral pro- 

 jections with enlarged knobs bent sharply dorsally. In this embryo 

 they show no tendency to become bilobed, as is seen in embryo II and 

 in later stages. It has already been suggested that this may represent 

 an individual variation. 



verschieden gebauter Bestandtheile hergestellt wird ; der eine von diesen, der un- 

 paare, wachst in der Medianlinie aus dem Epithel der Vereinigungsstelle der zweiten 

 Kiemenbogen aus, derselbe nimmt friihzeitig die belcannte Netzstructur an, der andre 

 paarige Theil wird durch zwei scblauchartige, ventrale Austiilpungen der vierten 

 Kiemenspalten, die etwas nacb innen convergiren, dargestellt; letztere verlieren 

 erst nacb der Verscbmelzung mit dem medianen Antbeil, der sicli allmahlicb nacb 

 binten Tersebiebt, ibre einfacbe Scblaucbforni und wandeln sicb iu ein Netz von 

 Zellbalken um. 



