THE DEVELOPMENT OF THE SALIVARY GLANDS IN MAN 35 



which defines the ectal border of the palate process from the roof of 

 the hitcral extension of the oral cavit}'. This ectopalalhie sulcus is 

 shown in Figs. 7-19, j-/. Behind the termination of the superior dental 

 ridge it deepens and receives the buccal sulcus laterally. A second 

 smaller sulcus, parallel to the ectopalatine and placed lateral to it, 

 e.xtends from the parotid plane to the region of the orbital angle 

 (Figs. 16-18, jj). In the 22 millimeter embryo this sulcus has 

 disappeared ; the ectopalatine is conspicuous in this embryo also, 

 and the line of the buccal sulcus is prolonged upon its lateral wall as 

 a low crest (Fig. 24, /). Viewed from below (Fig. 4) the greater part 

 of the buccal sulcus is seen to pursue a general sagittal direction with, 

 however, a moderate convexity laterad. In front and behind this 

 segment two shorter portions of nearly transverse direction complete 

 its trajectory; the cranial, extending mesad from the angulus oris 

 {24} , forms the cranial border of the area of union of the maxillary and 

 mandibular processes ; the caudal, which corresponds to the abrupt 

 descent of the sulcus, meets the main segment at a rounded angle. 

 Here, then, the sulcus undergoes a change of direction both in the 

 sagittal and in the horizontal planes, describing a curve wliich may 

 be designated the orbital angle. It marks the commencement of the 

 narrowing of the oral cavity towards the fauces, and in forms in 

 which the material has allowed the observation, corresponds to a 

 primitively broader portion of the orbital inclusion. In this region also 

 the inclusion is crossed by the buccal nerve. In the sections the buccal 

 sulcus is V-shaped, with the angle most acute in its caudal segment 

 and in the parotid region, while in the interval the fundus becomes 

 slightly rounded. Craniad to the parotid the floor of the mouth 

 presents a small convexity immediately mesad of the buccal sulcus. 

 This convexity is defined at its mesal border by a faint furrow. The 

 formation extends from the parotid to the angulus oris, being best 

 developed in the middle of its extent and diminishing towards its 

 extremities. A similar pro parotid convexity occurs in other forms, 

 suggesting a tendency to form a fold in this segment also of the 

 buccal sulcus, a tendency soon repressed, however, for in the 22 

 millimeter embryo there is no sign of the convexity. 



The parotid is attached to the buccal sulcus at about the middle 

 of its sagittal segment, with which it forms nearly a right angle. It is 



