SALIVARY GLANDS 



165 



these epithelial buds grow into the mesoderm, they may either bifurcate or give off 

 lateral branches, and in this manner all the ramifications of the ducts of the 

 compound racemose glands are produced. The blind extremities generally end 

 eventually in enlarged tubular or saccular dilatations. All the epithelium of the 

 gland-saccules and ducts is derived from the original epithelial sprout, while the 

 basement-membranes and connective tissue and blood-vessels of the gland are 



FlG. 208. A, LUNG-RUDIMENTS OF HUMAN EMBRYO OP ABOUT FOUR WEEKS, SHOWING THE BUD-LIKE 

 ENLARGEMENTS WHICH REPRESENT THE LOBES OF THE FUTURE LUNGS. (His.) 



Three buds are seen on the right side, two on the left. 

 B, LUNGS OF A HUMAN EMBRYO MORE ADVANCED IN DEVELOPMENT. (His.) 



derived from the surrounding mesoderm. The salivary glands and most other 

 glands of the mouth, and part of the pituitary body, which must also be reckoned 

 as a glandular development, are formed in this way by involution of the buccal 

 or stomodoeal ectoderm ; while the lungs, liver, pancreas, thyroid, thymus, and all 

 the small glands of the rest of the alimentary canal are formed of involutions of 

 the entoderm. The development of the teeth, 

 which also first make their appearance as 

 involutions of stomodoeal ectoderm (enamel 

 germs), will be described after their structure 

 has been dealt with (in the part of this work 

 which is devoted to Splanchnology). 



Salivary glands. The submaxillary 

 gland appears as an epithelial sprout from the 

 floor of the mouth towards the close of the 

 fifth week (Sudler), 1 and the sublingual rudi- 

 ment develops on its outer side in the ninth 

 week (Hammar).' 2 The parotid develops in the 

 lateral wall of the cavity in the angle between 

 the roof and floor of the primitive mouth. 

 When the cheeks are formed by the union of 

 the freed lip -portions of the mouth- opening, 

 its duct comes to open in the cheek. Accord- 

 ing to Hammar, Stenson's duct is not formed as an epithelial sprout, as in 

 the case of the other glands, but appears first at the end of the first month 

 as a groove in the position specified, which afterwards closes into a canal and 

 becomes separated from the cheek by the ingrowth of connective tissue. The 

 duct in the tenth week runs over the masseter to the back of the mandible, where 

 the epithelial buds are given off which form the secretory tubules of the gland. 



FIG. 209. LUNGS OF A HUMAN EMBRYO 



STILL MORE ADVANCED. (His.) 



Amer. Journ. of Anat. i. 1902. 



Loc. cit. 



