152 THE DISSECTION OF PIG EMBRYOS 



the surrounding epithelium and forming the trench from which this type of 

 papilla derives its name. At the same time, lateral outgrowths arise from the 

 bases of the epitheUal cones, hollow out and form the ducts and glands of Ebner. 



A B C ^ 



Fig. 158.— Diagrams showing the development of the vallate papilla of the tongue (Graberg in McMur- 

 rich). a, valley; 6, von Ebner's gland. 



The taste buds of the vallate papillae are also formed early, appearing in embryos 

 of three months. Foliate papilla probably appear at about six months. 



DEVELOPMElSfT OF THE SALIVARY GLANDS 

 The glands of the mouth are all regarded as derivatives of the .ectodermal, 

 epithelium. Their development has been studied recently by Hammar (V^at. 

 Anz., Bd. 19, 1901) and by Schulte (Studies in Cancer etc., N. Y., vol. 4, 1913). 

 Of the salivary glands, the parotid is the first to appear. Its anlage has been 

 observed in 8 mm. embryos, near the angle of the mouth, as a keel-hke flange 

 in the floor of the alveolo-buccal (i. e. jaw-cheek) groove (Hammar). The flange 

 elongates, and, in embryos of 17 mm., separates from the epithelial layer, form- 

 ing a tubular structure which opens into the mouth cavity near the cephalic end 

 of the original furrow. The tube grows back into the region of the external ear, 

 branches, and forms the gland in this region, while the unbranched portion of 

 the tube becomes the parotid duct. 



The submaxillary gland arises at 1 1 mm. as an epitheKal ridge in the alveolo- 

 lingual (i. e. jaw-tongue) groove, its cephalic end located caudal to the frenulum 

 of the tongue. The caudal end of the ridge soon begins to separate from the epi- 

 thelium and extends caudad and ventrad into the submaxillary region, where it 

 enlarges and branches to form the gland proper; its cephalic unbranched portion, 

 persisting as the duct, soon hollows out. 



The sublingual and alveolo-lingual glands develop in 24 mm. embryos as several solid 

 evaginations of epithelium from the alveolo-lingual groove (Fig. 163). Each group, usually 

 regarded as a sublingual gland, really consists of the sublingual proper, with its ductus major, 

 and of about ten equivalent alveolo-lingual glands. 



The solid branched anlages of the salivary glands last become hollow at their tips. 

 The glands continue to differentiate until after birth. Mucin cells may be distinguished 

 by the sixteenth week and acinus cells in the parotid glands at five months (McMurrich). 



