534 H. H. SWINNEETON. 



mandibular and symplectic^ wliich is not indicated in any 

 other way — not even by any sign of the sharp bend present 

 in the adult (fig. 23^ hym., sym.). The axis of the plate pro- 

 jects obliquely forwards and downwards from the auditory 

 capsule, but not at so great an angle as in the later stages. 

 Perhaps it is in association with this that the line of attachment 

 to the auditory capsule, instead of being horizontal, is almost 

 vertical, and it is not marked by any change of structure 

 indicative of a future articulation, but hyoniandibular and 

 capsule together form a continuous whole (fig. 41, au. c. hym.). 



In the mandibular arch the quadrate (qii.) and Meckel's carti- 

 lage {mh.) are already marked off by definite signs of chon- 

 drification from the dense tissue which lies between them. 

 Anteriorly and posteriorly the quadrate passes imperceptibly 

 into pro-cartilaginous processes. The former, the palatine 

 process {qu. pa.), is long and slender, and extends halfway 

 towards the free end of the adjoining trabecula ; from its 

 fellow of the other side it is proportionately more widely 

 separated than at any later stage. The latter, the 

 metapterygoid process {qu. 7n.), is stouter, and lies with its 

 lower border close to, and parallel with, the upper border of 

 the symplectic. 



Meckel's cartilage, as regards its general shape, is com- 

 parable to that of Stohr's Embryo No. II (83, p. 10), but as 

 regards completeness of chondrification it more closely 

 resembles his larva No. IV. In shape it is slender, and 

 meets its fellow in the middle line (figs. 1, 6, mJc.) without the 

 intervention of pro-cartilage. 



Thus the general developmental processes of the first two 

 visceral arches agree closely with those of the salmon, but in 

 the time at which these take place there is a considerable 

 difference. Here, as with the fore-part of the auditory 

 capsule, there has been some influence at work hastening 

 events. Thus, whilst the branchial arches at this stage are 

 comparable with those of Stohr's youngest embryo, these two 

 arches, by the absence of pro-cartilage between symplectic 

 and hyomandibular, and the elements of the mandible; and 



