234 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



constricted at its base. It projects horizontally from the sloping 

 dorsal wall of the buccal sulcus, a short distance from its fundus. 



The attachment retains the form of a short longitudinal keel, com- 

 posed of cells resembling the basal cells of the oral epithelium, until the 

 embryo has attained a length of 31 millimeters. In all these embryos 

 it closely resembles that just described in the embryo of 21 millimeters, 

 craniad minute, of semicircular cross-section, gradually broadening 

 caudad; the terminal sections regularly show a constriction at the 

 base, which deepens as the free duct is approached. This has an 

 increasingly long horizontal segment, and shows for a time a slight 

 bend, where its direction becomes pronouncedly ventrolateral, which 

 appears to correspond to the junction of the sprout with the primitive 

 flange. This gradually is effaced as development proceeds. As long 

 as the caudal segments of the keel are constricted, we may infer that 

 portions of it are being added to the free duct. In the 34 miUimeter 

 embryo the character of the attachment has assumed its definitive 

 form. It is now circular and a lumen is present. The duct has come 

 to rest, except in so far as the position of its orifice may be altered by 

 changes in the oral cavity itself. 



The character of the parotid attachment in the embryos of 20 

 millimeters to 31 millimeters is plainly that of a keel formed by the 

 proliferation of the basal cells, without the intervention of a fold or 

 fissure. This fact supports the view wc have taken of the formation 

 of the duct at the border of the flange, viz. that from the first we have 

 been dealing with a process of proliferation advancing along the edge 

 of a sohd fold. Taking origin at the widest part of the flange, in 

 successive stages it extends craniad, involving ever narrower portions of 

 the flange. Eventually it reaches the end of the fold and thence 

 continues its advance along the oral epithehum. Pari passu the 

 flange undergoes destruction in a caudocranial direction until in the 

 embryo of 21 milhmeters it has wholly disappeared. That the flange 

 itself is prolonged craniad during this process seems highly probable ; 

 as long as the fissure existed the possibility was given; yet the presence 

 of the fissure does not of itself prove the reality of the advance, for 

 in the transition from flange to open sulcus, the presence of an inter- 

 mediate region with a fissure is a physical necessity. The point loses 

 importance in view of the fact that the whole process of the formation 



