DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 221 



pars cylindrica (8) slopes ventrad, caudad, and mesad towards the oral 

 epithelium, which it approaches ventrad of the secondary buccal sulcus 

 (la) near its termination. Thisrelation to thesulcus is duemerelyto an 

 increase of the early dislocation of the inclusion from its fundal posi- 

 tion. The sulcus has been carried dorsad as the palatomandibular 

 plane has continued to enlarge, forming a new fundus at a Irigher 

 level, the secondary buccal sulcus; while the orbital inclusion repre-, 

 sents the earlier and more v-entrally placed fundus of the buccal sulcus. 

 In this embryo the cranial process is short and does not reach the deep 

 facial vein. In others of about the same stage, where the cranial 

 process is longer, the tip lies close to the oral epithelium. The dis- 

 placement of the inclusion is greatest at the junction of the pars lata 

 and pars cyUndrica, where it was initiated, and thence diminishes cra- 

 niad and caudad. In later stages the whole inclusion is gradually ap- 

 proximated to the internal pterygoid. Inclusions with longer cranial 

 processes may extend beyond the pterygoid under cover of the masseter 

 and the deep facial vein. Such are not uncommon in embryos pf i8- 

 20 millimeters. In many of these, however, and regularly in later 

 stages, the cranial process is short and blunt. 



On separation the pars lata rather quickly assumes a circular sec- 

 tion. There is no loss of substance in this change, nor evident de- 

 forming force, for the inclusion is everywhere surrounded by mesen- 

 chyme and in contact only with the buccomasseteric nerve. It would 

 seem, therefore, an effect of something akin to surface tension at the 

 junction of the inclusion with the mesenchyme. The growth of the 

 inclusion after separation continues at about the same rate as the 

 lengthening of the sulcus that has given rise to it. The pars lata, dis- 

 tinguishable by its larger section and its contact with the bucco- 

 masseteric nerve, still is found opposite the orbital angle. The pars 

 cylindrica extends along the greater part of the secondary buccal sulcus. 

 From an early stage (12 millimeters) there has been a small segment of 

 the sulcus caudal to the end of the inclusion. This lengthens pro- 

 gressively both before and after separation of the pars cylindrica. 

 There is no way of telling after separation whether any of the relative 

 gain of this segment is due to a diminished rate of growth in the inclu- 

 sion. The disparity in size between the pars lata and the pars cylin- 

 drica is gradually effaced. After assuming a cyhndrical shape, the 



