DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 27 1 



sprout begins its distal growth. The comparison again suggests that 

 sulcal position, when accompanied by the formation of a flange, 

 accelerates the development of the sprouts. 



The comparison of the 28 millimeter and 31 millimeter embryos is 

 illustrative of the variations in the rate of growth, so frequently ob- 

 served in the development of the salivary glands. 



The 34 and 35 millimeter embryos show a continuation of the same 

 processes. In the latter the first orbital is relatively small (Fig. 107, 20) 

 and situated close to the border of the masseter. The second is of larger 

 size and of almost vertical direction. The third is also directed dorsad 

 and of a size about equal to the first. In all the other embryos 

 of our series the first orbital is appreciably the largest of the series. 



Important changes in the topography of this portion of the mouth 

 are now initiated, a vertical portion of the cheek is forming with the 

 reduction of the buccal sulcus and the appearance of superior and in- 

 ferior alveobuccal furrows. The vertical wall of the cheek defined 

 by these sulci diminishes in height caudad, and in the plane of the 

 second orbital the inferior sulcus ascending towards the superior be- 

 comes shallow and finally disappears, without reaching the funnel- 

 shaped contraction of the faucial region. The secondary buccal 

 sulcus persists, and to its dorsal wall are attached the tliird and second 

 orbital sprouts, craniad of which it becomes continuous with the 

 superior alveobuccal sulcus. Just ventrad of tMs sulcus the wall of 

 the cheek presents a convexity to the oral cavity, the anlage of the 

 ridge upon which the parotid and, -subsequently, the orbitals open. 

 It is as yet of small sagittal extent and does not reach the first orbital, 

 which is attached to the cheek in line with the ridge, but caudal to it. 

 About midway between the parotid arid first orbital, on the left side, 

 an orbitoparotid springs from the oral epithelium, close to which 

 it turns caudad, taking the direction of the orbital elements (Figs. 106- 

 108, 17). This behavior of the orbitoparotid is again suggestive of a 

 primitive continuity of the orbital and parotid series. 



In the 51 millimeter embryo the stomal ridge has extended caudad, 

 and now all three orbital ducts are attached to its summit, in line with 

 the parotid orifice, which is at its cranial extremity (Fig. 109,20-22). 

 After a course along the ridge, for a distance diminishing from the 

 first to the third, they cross the secondary buccal sulcus and enter 



