108 ME. W. G. EIDEWOOD ON THE H.TOBEANCHIAL 



In the hyoid arch the absorption has been greatest towards the 

 ■median extremity, so that the cornua taper inwards to a point 

 which is still connected by a very ill-defined tissue with the axial 

 structures. A new cartilage, as yet but faintly outlined, is 

 appearing between the inner ends of tbe hyoid. cornua, and tends 

 to convert the notch or indentation at the front of the hyo- 

 branchial apparatus into a foramen. The larynx now completely 

 overlies the developing thyrohyals, and its most anterior point is 

 situated exactly over the middle of the median bar or isthmus 

 between the thyroid foramina. 



Stage V. (PI. 11. fig. 8.) 

 The ceratobranchials have completely disappeared at this stage, 

 and the thyroid foramina have been converted into deep clefts 

 between the alee in front and the thyrohyals behind. Both alae 

 and thyrohyals are now sharply outlined, and the whole apparatus 

 has begun to assume the peculiar aspect of the hyobranchial 

 skeleton of the adult. The alae are racket-shaped. The hyo- 

 glossal notch has been converted into a complete foramen (fig. 8, 

 Ji) by a further development of the cartilage which in Stage IV. 

 was beginning to make its appearance between the median ends 

 of the hyoid cornua. The new cartilage has assumed a definite 

 outline and tapers anteriorly to a blunt point. The ceratohyals 

 themselves are only to be recognized as vestigial cartilages, blunt 

 externally and pointed at their inner ends, situated behind and 

 internal to tbe articular end of Meckel's cartilage. It is here 

 worthy of remark that the absorption of the hyoid cornua has 

 proceeded in a most regular manner from the median end out- 

 wards, the last remnant to disappear being the external extremity. 

 There is nothing to be recorded with regard to the laryngeal 

 skeleton except that it has been gradually increasing in size, and 

 that its diameter is now as great as the distance between the 

 centres of the alary cartilages. 



Stage VI. (PI. 11. fig. 9.) Embryos toith no tail, or with the merest 



remnant of it. Length of hody about 14 mm. Length of 



hind limb lohen extended 10 or 11 onm. Fore limb 6 oiwi. 



Although the embryos at this stage are still comfortably 



ensconced in the maternal integumeatary pits, the hyobranchial 



skeleton does not differ materially from that of the fully-grown 



adult, the most important differences being that the thyrohyal is 



