Mervin T. Sudler 409 



bryo of a neck-breach length of 1-1 mm. (six weeks). Hammar " found 

 it in an embryo 13.2 mm. long and His " in one 13.8 mm. long. In 

 regard to the parotid Hammar states that he has found it at the 

 end of the first month and that it does not appear as a solid rounded 

 rod as generally described but as a groove which eventually closes off 

 and forms the duct of the gland. His states that it appears at 7^ 

 weeks and Chievitz found it at the end of the 8th week. Hammar 

 found the sublingual at 9 weeks and Chievitz states that he observed it 

 a little before the rudiment of the parotid appeared, which Avould mean 

 early in the 8th week. 



In this series of models the submaxillary gland first appears in that 

 of embryo CXLIY, where it is simply a rounded rod of cells staining 

 deeper than the surrounding tissues. This embryo has a neck-breach 

 length of 14 mm. In the model of embryo XLIII it is quite a large 

 rudiment, as seen in Fig. 9. It is a straight cylindrical shaft with a 

 knob turned directly away from the middle line. It meets the mouth 

 cavity at the angle where the tongue and the ridge separating it from 

 the groove of the mandible meet. It is a solid object throughout. In 

 the model of the oldest embryo studied, embryo XXII, it has grown 

 larger and the bulbns end has grown into an oval-sha])ed bodv covered 

 with rounded enlargements marking the future lobes of the gland. It 

 is still solid and the connective tissue around it shows a slight conden- 

 sation into a capsule. No other salivary gland was observed at this 

 stage. 



Thymus Gland. 



Stieda in 1881 was the first to observe that the thymus gland origi- 

 nated from a visceral pouch. Then came Born's important contribu- 

 tion stating that it arises from entoderm. This has since been con- 

 firmed by Prenant/^ Mall '" and His. 



Beard" worked on a complete series of Eaja embryos where the 

 thymus develops from the first four branchial clefts, while a rudimen- 

 tary thymus makes its appearance on the fifth. In this case the rudi- 



J^Loc. cit. 



i*Loc. cit. 



15 A. Prenant: Contribution h V etude du development organique et histologic du 

 thymus, etc. La Cellule, 1894. 



"^F. P. Mall: The branchial clefts of the dog with a special reference to the 

 origin of the thymus gland. Studies from the Biological Laboratory, Johns Hop- 

 kins University, Vol. 4, No. 4, 188S. 



17 J. Beard: The Development and Probable Function of the Thymus. Anat. Anz., 

 Bd IX, 1894. 



