MAMMALIAN ALVEOLINGUAL SALIVARY AREA 343 



duced to rudiments and the caudal sprout accelerated, we should have 

 an anlage resembling that of the sublingualis major, where a sprout 

 of caudal position is continued forward by an epithelial keel. In the 

 case of this gland in the cat, there is a late efflorescence of the duct 

 with small sprouts, which could be interpreted as a late assumption 

 of glandiferous activity on the part of the retarded and coalesced 

 elements of the keel. In this connection it is interesting to note that 

 the keels are not always formed continuously from behind forward, 

 but small outlying fragments may appear in line with, but in advance 

 of, the extremity of the main keel, which thus presents discontinuities 

 in its proliferation, as though its elements retained some indepen- 

 dence. Such interruptions are infrecjuent, but occur in the keel of 

 the Bartholinian element on both sides in the human embryo of 20 

 millimeters, and in the subma.xillary on one side. They also have 

 been observed in the keel of the subma.xillary in the cat. This is in 

 brief the developmental evidence, which prompts the interpretation 

 of the larger keeled salivary glands in terms of a series of simple glands, 

 rather than as hypertrophied equivalents of individual elements. 

 The line of advance of a duct would thus appear as a selected strip, 

 crystallized, as it were, out of a more primitive diffuse field. The pres- 

 ence of a sulcus, or, more particularly, a flange, would appear as an 

 accelerating factor in the development of sprouts, rather than a neces- 

 sary condition of such an organization as is here contemplated, for the 

 flanged glands (submaxillary, parotid) anticipate in appearance and 

 exceed in development the glands which are only fjrovided with keels 

 (sublingualis major, orbitals I, II, III), but agree with them in the 

 formative process, which for both is proliferation, advancing craniad for 

 the pro.ximal portion of their ducts, proceeding distad into the mesen- 

 chyme for the remainder of their epithelium. The comparative evi- 

 dence for this view, which is abundant, has been presented elsewhere 

 (Huntington). 



We thus conceive the gland field of the alveolingual gutter organized 

 into sagittal glandiferous lines, mesal the submaxillary, intermediate 

 the sublingualis major, while laterad persists the diffuse gland field of 

 the lesser sublinguals, in which organization has proceeded no farther 

 than the abortive keel, which connects the early members of this 

 series. It might be expected that such divisions as these would not 



