1901.] NATURAL SCIENCES OF PHILADELPHIA. 243 



copula. In its outer portion the hyoid turns sharply upward to 

 form au ascending process, which articulates with the quadrate. 



In its anterior portion — i.e., where the processus articularis is 

 given off — the quadrate is joined to the ti*abecula of the same side 

 by an ascending bar of cartilage, the commissura quadrato-cranialis 

 anterior (Gaupp) or palato-pterygoid bar. Posteriorly again the 

 quadrate bends sharply upward and then as a stout bar (processus 

 ascendens, fig. 19, Pi-.A.) extends inward back of the eye and in 

 front of the auditory capsule to join with the trabecula just in 

 front of the basilar plate (parachordal). There is no distinct 

 separation between these connected cartilages, the matrix of each 

 being perfectly continuous with that of the others. 



It now remains to connect the conditions observed in the present 

 stage with those seen in the preceding. The chief differences 

 between the former and the latter are briefly these: (1) The rela- 

 tively much greater length of t?e " diverticulum," a condition asso- 

 ciated with the removal of the part connecting it with the 

 pharyngeal wall to a point more posterior, i. e. , back of the quadrato- 

 hyoid aiticulation; (2) the reduction in size of the middle portion 

 of the " diverticulum," and (3) the almost complete obliteration 

 of the ventro-anterior portion of the hyomandibular fold. 



These ditferences are, I believe, correlated with a continuation of 

 the same processes treated of under the description of the pre- 

 ceding stage. These are chiefly the modifications undergone by 

 the neighboring muscles and cartilages. The general growth of 

 the animal has had little, if anything, to do in producing the 

 differences between the two stages. There has been a considerable 

 increase in width of the head — an increase in which, however, the 

 contained structures have taken part. The greatea* length of the 

 " diverticulum " has been produced by the continued increase in 

 depth of the depression in the distal border of the fold. In stage 

 III this depression was relatively shallow, so that the " diverticu- 

 lum " was very short and blunt. In the present stage the 

 " diverticulum " is very long, having the form of a long, narrow 

 cord somewhat expanded at its distal extremity. The insinking 

 of the disial border was associated with the growth of the depressor 

 raaudibulse, in consequence of the latter' s acquisition of a point of 

 attachment to the quadrate in front of and below the distal border 

 of the hyomandibular fold. In the present stage this muscle has 



