214 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



orbital segment of the buccal sulcus, in view of its non-existence in em- 

 bryo No. 1 20, appears rather to represent a cranial addition to the 

 sulcus than the result of locally accelerated growth. In the 11 milh- 

 meter embryo the orbital inclusion is still quiescent, while the sulcus 

 craniad of it has continued to lengthen. From this period the orbital 

 fold, which in embryos of 8.5 millimeters to 10.5 millimeters advanced 

 at a rate far exceeding that of the lengthening of the buccal sulcus, 

 and for a moment approximately reached the angulus, is no longer 

 able to maintain the balance of growth in its favor and henceforth 

 undergoes a relative caudal displacement. Further, it is to be noted 

 that in the four younger embryos of this series the pars lata does not 

 increase in size and that, therefore, the advance of the fold for the time 

 being has come to a standstill. In comparing the 11 and 11. 5 milli- 

 meter embryos one or two points require comment. In this period 

 the pars cyHndrica has lengthened one-half. On account of the ob- 

 liquity of the pars cylindrica which is attached to the terminal ento- 

 masseteric segment of the buccal sulcus, this element is considerably 

 underestimated in section counts, while the pars lata involving the 

 beginning of the sagittal segment receives nearly its full value. In 

 reconstructions made of 11.5 and 12 millimeter embrj-os it was found 

 to be no longer than the pars cyHndrica. From this period the pars 

 cyHndrica lengthens more rapidly and in later stages many times 

 exceeds the length of the pars lata (Fig. 45). The rate of growth in 

 the pars cylindrica is such as to maintain its parity with the sulcus 

 to which it is attached, except at its extreme caudal end. Here it 

 gradually lags a Httle behind the sulcus, which acquires a short termi- 

 nal segment that never becomes folded. 



The general features of the buccal sulcus at 11 .5 milHmeters are shown 

 in Figs. 23-30, a series of sections from embryo No. 256 which corre- 

 sponds closely with No. 251. Its trajectory comprises a rather abrupt 

 sweep mesad from the angulus (Fig. 23, 2), a gradual ascent in nearly a 

 sagittal direction to the orbital angle (Fig. 27), and there a second 

 change of direction to its oblique terminal segment. The maxilloman- 

 dibular plane is ventrolaterally inclined at the angulus oris (Fig. 23), 

 nearly horizontal near the orbital angle (Fig. 26), while caudad it is al- 

 most wholly reduced to form the pars cyHndrica (Fig. 27). The epithe- 

 Hum is thickened at the fundus of the sulcus. On the floor it thins 



