212 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



(Fig. 22) all its dimensions increase, especially its breadth. In the 

 region of the mandibular nerve a remnant of the fissure still indents 

 the base of the pars cyUndrica ; in more cranial sections the fold is 

 laid open in its entire breadth by a narrow cleft, which, becoming 

 wider, causes the fold to disappear a short distance from the angulus 

 oris. This broad cranial addition to the fold is the pars lata. 



In the embryo of 10.5 miUimeters the orbital fold attains its maxi- 

 mum relative to the buccal sulcus. Caudad for a section or two the 

 sulcus is uninvolved ; craniad the fold extends beyond the postangular 

 bend into the postangular segment, failing, but only just faihng, to 

 reach the angulus itself. In running over the sections in a cranio- 

 caudal direction, we meet in the same plane as the angulus the pars 

 lata, with a narrow fissure extending through its whole breadth ; 

 the walls of the fissure then come into contact, and a solid flange with 

 a pale axial Une of periderm is seen, its base indented by a remnant 

 of the fissure ; the flange then narrows, and a constriction, appearing 

 at its base, becomes circular in section. The process being progres- 

 sive caudocraniad, the e\-idences of folding and constriction are most 

 marked in the plane of the mandibular nerves. Of the orbital fold 

 itself, about half corresponds to the pars cylindrica, about half to the 

 pars lata. Their junction is effected by gradual transition near the 

 point where the small buccomasseteric nerve comes into close contact 

 with the oral epithelium. The orbital inclusion retains its relation 

 to the buccomasseteric nerve as late as in the 70 miUimeter embryo. 

 In embryos of 20 millimeters and less the contact is intimate, appar- 

 ently no mesenchvnne intervening. 



In immediately succeeding stages the orbital inclusion becomes 

 separated from the angulus oris by an increasing length of unfolded 

 buccal sulcus. This segment of the sulcus appears to be an addition 

 from in front. It meets the older region of the sulcus at an appre- 

 ciable though rounded angle, which I have called the orbital angle. 

 This, it will be remembered, is characterized not only by a change 

 of direction in the horizontal, but in the vertical plane as well. It 

 forms the crown of the sagittal arch of the sulcus and corresponds to 

 the junction of the pars lata and cylindrica of the orbital inclusion 

 and to the crossing of the buccomasseteric nerve. This nerve is now 

 the most available landmark in this region, for already the mandibular 



