564 



ceratobrauchial *), and anterior to tlie point where the united bases 

 of the cartilaginous rods of the first and [second vagus arches join 

 the cartilage of the glossopharyngeal arch. 



Fig. 8 shows the position of this group of cells. They are dis- 

 tinguishable from surrounding mesenchyme merely by their closer 



- ep 



ep hr add th st add th 



Fig. 8. Cross-section through the thyroid Anlagen in an embryo 19 mm long, add 

 adductor arcuum hranchialium. ep br epibranchial cartilage of the first branchial 

 arch, st sterno-hyoideus. th cells of the thyroid Anlage grouped above the adductor 

 muscle. 



grouping. In an embryo of 21 mm, one or two small vesicles are 

 found where the group of cells marked th lie in fig. 8. These 

 vesicles increase in number as the embryo grows until in the little 

 amphibian of 46 mm, they constitute a considerable mass of vesicular 

 tissue , still occupying the same position in relation to surrounding 

 structures. 



The Suprapericardial Bodies. 

 In fig. 9, from an embryo of 15 mm, the origin of the supra- 

 pericardial bodies is shown. They lie on either side as a small 

 vesicle immediately below the floor of the branchial chamber, with 

 which they are still connected by stems, although the stem of the 

 right vesicle alone falls in the plane of the section. They are formed 

 by a single layer of yolk-laden cells whose nuclei are near the surface 

 of the vesicle, while the yolk granules are aggregated at the centre. 

 The section passes through the second vagus cleft, or fourth branchial, 

 counting the hyomandibular as the first. There is consequently one 

 cleft posterior to that of the section, namely: the third vagus cleft, 



1) These cartilages are named from Wiedeesheim'b "Vergleichende 

 Anatomie". There is no attempt at homology on the part of the author. 



