2/0 DEVELOPMENT OF SALIVARY GLANDS IN THE DOMESTIC CAT 



orbital and the secondary buccal sulcus. The attachment is a short 

 keel, fundal in position, constricted at its base, and extending craniad 

 to the angle between the second orbital and the sulcus. It is interest- 

 ing to note that on the right side of tliis embryo, each member of this 

 series bears to the precechng member a relation almost identical with 

 that borne to the parotid by the orbitoparotid, when it occupies the 

 angular position. 



The 31 millimeter embryo is but little more advanced. Three 

 orbital elements are present on each side, diminishing in size caudad, 

 and all are now attached to the roof of the oral cavity well mesal 

 to the fundus of the buccal sulcus. The first is represented by a keel, 

 which becomes constricted at its base and is finally continued into a 

 free cord of cells as it is followed caudad. The anlage is sohd through- 

 out. It diverges dorsad and laterad at a very acute angle from the 

 oral epithehum, a small quantity of mesenchyme intervening, and 

 terminates opposite the beginning of the second orbital in a slightly 

 enlarged extremity. The total length is 285 1^, of which 120 /^ are 

 free. The anlage lies craniad of the facial vein, except for its caudal 

 sections. The keel now overlaps the dental ridge for 225 m. 



The second orbital begins as a keel in the angle between the free 

 extremity of the first and the oral epithehum. It has a total length 

 of 180 M, of which 90 fj. are free. The anlages overlap for 30 ^, and the 

 second is sHghtly mesal in position. In structure and direction it is 

 an almost exact copy of the first, and lacks the thicker sprout of the 

 28 millimeter embryo. The mesenchyme in which it lies is widely 

 continuous with that of the orbit. The deep facial vein Ues lateral 

 to, it, and between them appears the cranial extremity of the orbital 

 inclusion. The third orbital bears nearly the same relation to the 

 second that the second bears to the first, inserted between its fundus 

 and the oral epithelium, shghtly to the mesal side. Its total length 

 is 45 M, of which 15 /x are free. It is overlapped in its whole extent by 

 the second orbital. 



These three elements appear to have essentially the same history, 

 their anlages appearing as soUd keels which are subsequenth' freed by 

 constriction; they differ collectively from such keeled glands as the 

 parotid and submaxillary in the late appearance of an actively growing 

 sprout, so that the keel here makes a long advance before the sluggish 



