THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 3 1 



rise to variant sprouts, orbitoparotids, whicii in turn may give rise 

 to inclusions. 



The following series of human embryos covers the period from the 

 latter part of the first to the end of the third month of gestation. It 

 permits us to observe the changes in the buccal sulcus from the first 

 appearance of the orbital inclusion to the establishment of the parotid 

 in its definitive position. There are, however, gaps in the series, the 

 most inconvenient of which is perhaps that between Hammar's 

 embryo of 11.7 millimeters and that of Paulet of 14.7 millimeters. 

 This appears to be the critical period in the formation of the parotid 

 fold of Hammar, the evidence for which, I believe, is still incomplete 

 so far as the human embryo is concerned. 



1. Hammar. Embryo of 8 millimeters, N.L., end of first month. 

 Near the angulus oris is a sUght pouting {Ausbuchtimg) of limited 

 extent. 



2. Columbia Collection, No. 229. 7.5 millimeters, N.B., measured 

 after fixation in formalin. Obtained by Dr. A. J. Brown. The epider- 

 mis and oral epithelium are in many places separated from the base- 

 ment membrane. The left side of the head is damaged ; on the right 

 the general outlines of the oral epithelium are well preserved. The 

 sections are very obliquely frontal in the head region. The buccal 

 sulcus draws rapidly away from the surface in the first portion of its 

 course as it sweeps mesad across the area of union of the maxillary 

 and mandibular processes, becomes more nearly sagittally directed in 

 its caudal half, and finally disappears as the first entodermal pouch is 

 approached. Ftom the angulus oris for five sections of 13.3 fi. a marked 

 thickening of the epithehum is found at the fundus and extending 

 into the dorsal wall of the buccal sulcus (Fig. 2,7). The sulcus itself 

 is widely open to the oral cavity, but presents a perceptible narrowing 

 opposite the mesal hmit of the epithelial thickening. From the 

 angulus oris caudad the thickening diminishes and comes to occupy 

 mainly the dorsal wall of the sulcus; coincidently the constriction 

 becomes more pronounced. In the six sections caudal to the thicken- 

 ing (the 6-1 ith behind the angulus oris) a fold is clearly defined. 

 In the 8th and 9th sections it is closed (Fig. 3,3); a nearly circular 

 mass of cells with a small central lumen appears in the sections, con- 

 nected to the oral epithelium by a rather narrow pedicle, through the 



