234 PROCEEDINGS OF THE ACADEMY OF [Maii^h, 



have sucli a section, in which, however, the phiue is lower on the 

 light, side than on the left. Commencing below, we observe on the 

 right of the figure a short, blunt diverticulum of the pharyngeal 

 Avail, extending outward and slightly forward between the Anlaf/en 

 of the mandibular and hyoid cartilages. This part corresponds 

 to broad proximal portion of the fold shown in fig. 11 as continu- 

 ous with the pharyngeal wall. In the fourth section dorsal to this 

 (fig. 17) the same portion of the fold is still seen, and just exter- 

 nal to its distal extremity is an elongated strand of like nature 

 (Tt/m.'), somewhat swollen in its outer portion, where it terminates 

 just beneath the external epithelium. This part is the swollen 

 poriion of the cleft, which, as already mentioned, extends out in 

 front of the hyoidean muscles and forms the distal expanded por- 

 tion of the cord-like extension of the fold. In the second section 

 above this (fig. 18) these two parts of the fold join, so that it now 

 appears continuous throughout [Ht/n.). The present section gives 

 a very good view of the course taken by the hyomaudibular fold. 

 One will observe that it has a very broad origin from the pharyn- 

 geal wall, and that from this point it extends outward and also 

 considerably forward. In its middle portion the fold is consider- 

 ably constricted, while in its distal outer extremity it is enlarged to 

 form the swollen, bulbous portion which curves outward in front 

 of the hyoidean muscles, as is well shown in the figure. 



One notices that in fig. 18 the outer, distal extremity of the 

 fold is farther removed from the exterior than in fig. 17. If the 

 left side of fig. 16 {Hym.) — which represents a plane slightly 

 more dorsal than that of the right of fig. 18 — be now consulted it 

 will b3 seen that this portion is still farther removed from the 

 exterior, and by comparing the same fold (^Hym.) in the following 

 two figures (17 and 18) the distance between the two will be seen 

 to be still more increased. In the latter two figures the fold 

 approaches very closely the proximal portion of the second visceral- 

 cleft {3 V.J.) — a feature to which we have already called attention. 



Bringing together the facts so far obtained relating to the third 

 stage, we shall now endeavor to form a conception of the hyoman- 

 dibular fold as a whole. It arises as a solid fold of the wall of 

 the pharynx and extends downward and obliquely forward as a 

 thin plate between the first and second visceral-arches. Its origin 

 from the pharynx extends downward and forward, beginning above 



