586 Uil. W. G. Ill OB WOOD ON THE HYOBRANCllIAL [May 18, 



beginning. The hyoiJean constituents are sliglitly larger than 

 before, and the branchial are smaller. There is still a triangular 

 space on either side of the basihyal : the spicula of the cerato- 

 brauc-hials are shortening up. The most interesting feature to be 

 noted in this stage is the fenestration of the hypobrauchial plate 

 in those regions situated immediately over the thyroid bodies. 

 The cartilage in the area marked tf. in fig. 3 is extremely thin, and 

 becomes converted into a distinct perforation in Stage 4. The 

 postero-internal margin {t) of the incipient foramen soon 

 becomes rod-like. It enlarges rapidly, and when, later, the 

 absorption of the external boundary causes the thyroid foramen 

 to open latei-ally, it becomes recognizable as the thyrohyal 

 {t, ligs. 4-7). When recounting recently the mode of develop- 

 ment of the hyobranchial skeleton of Pipa, it was with 

 considerable hesitation that I described (16. p. 106 et seq.) the 

 thyrohyals as persistent parts of the hypobranchial cartilage left 

 by the perforation of the plate and the subsequent conversion of 

 the foramina into deep sinuses. This view of the mode of 

 development was so opposed to all preconceived notions that it 

 seemed little short of heresy to give expression to it, and it was 

 only after repeated examinations of the specimens that I could 

 bring myself to publish the observation. The present discovery 

 of a similar origin of the thyrohyals in a less aberrant type of 

 Batrachian not only confirms my foruier view, but opens up the 

 bro:ider question whether, after all, this may uot be their normal 

 mode of development in Anura. A glance at figs. 3, 4, and 5 

 shows that the thyrohyals are terminated by those processes 

 which, following Gaupp, I interpret as the spicula of the fourth 

 branchial arch. These might easily be mistaken for the free ends 

 of newly outgrowing thyrohyals, although, as a matter of fact, 

 they are absorbed with the ceratobranchial cartilages, leaving the 

 extremities of the true thyrohyals freely exposed. And thus 

 become reconciled the apparently conflicting views of Saint-Ange 

 (17. pp. 410 and 417), who considers the thyrohyals as the 

 persistent spicules of the fourth branchial arch, and Cuvier (3. 

 p. 397), Eathke (14. p. 39), Duges (4. pp. 99, 101, 102), Stannius 

 (19. p. 65), Gotte (6. p. 332), Parker (11. pp. 164, 170, 171, 185, 

 and 12. p. 259), and Gaupp (5. pp. 422 and 433), who regard them 

 as outgrowths of the hypobranchial plate situated behind and to the 

 mesial side of the fom'th branchial arch. The alternative view that 

 the thyrohyals of Anura are persistent ceratobranchials has been 

 supported by Eeichert (15. pp. 59 and 258), by Owen (10. p. 90), by 

 Parker, who in his textbook (13. p. 173) unfortunately departs 

 from the views expressed in his memoirs {I. c.) and states that the 

 thyrohyals are the fourth ceratobranchials, and by Walter (21) 

 and Cope (2. p. 23-1), who accept Parker's determination without 

 reserve. Stdhr (20. p. 84), also, ventures upon a positive 

 statement in favour of the thyrohyal being the ventral or proximal 

 end of the fourth branchial arch ; and that he does not mean by 

 this the hypobranchial constituent of the arch is evident from his 



