242 PROCEEDINGS OF THE ACADEMY OF [March, 



blends with the wall of the pharvnx dorsal to the inner opening 

 of the first branchial- cleft. 



To recapitulate briefly the state of the hyomandibular fold at 

 the present stage : we have found the ventral portion of the fold 

 present only as an inconspicuous protrusion of the veutro-lateral 

 angle of the pharynx. Only the dorsalmost portion of the orig- 

 inal fold is well developed, and from this tlie greatly prolonged 

 "diverticulum" extends forward as a solid coi'd of cells. The 

 latter originates posterior to the quadrato-hyoid articulation. 

 Throughout the greater part of its length the cord is closely ajiplied 

 to the outer surface of the processus muscularis. Anteriorly, 

 however, it bends sharj^ly outward in front of the depressor ossis 

 hyoidei and terminates blindly as a somewhat bulbous enlargement 

 in the subcutaneous tissue. 



I may here describe briefly the condition of the neighboring 

 skeletal structures, since in the present stage these have acquired 

 the relations which they retain throughout the entire larval period. 

 The animal has now passed beyond the pro-cartilage stage and 

 consequently the cartilages can be readily traced. In most cases 

 they already show a well-defined perichondrium. The quadrate 

 cartilage is prolonged in an an tero- posterior direction almost parallel 

 with the corresponding trabecula cranii. Its course is thus quite 

 the reverse of that which characterizes its adult condition. Its 

 distal articular end is prolonged as the jirocessus articularis down- 

 ward and forward to a point beneath the anterior surface of the 

 eye and at a later period still farther forward. At its distal 

 extremity it bears the transversely placed mandibular cartilage 

 (Meckel's). The greater part of the quadrate is prolonged 

 upward and outward as a stout plate immediately underlying the 

 orbit — the processus muscularis — to the outer side of which are 

 attached the depressor mandibular and depressor ossis hyoidei. In 

 the concavity formed in the inner (and upper) surface are lodged 

 the muscles of mastication (fig. 24, k.m.). On the ventral surface 

 near the point of junction between the body of the cartilage and 

 the processus muscularis there is forming at the present stage a 

 shallow, concave articular surface for the head of the hyoid car- 

 tilage. The latter is a stout bar of cartilage extending trans- 

 versely beneath the floor of the pharynx and joined to its fellow 

 of the opposite side by the intervention of a median plate, the 



