1898.] HTOID OF ALYTE8 OBSTETEICAXS. 11 



the rod. The ventral splint-bone has also begun to ossify. The 

 ceratohyal is extremely slender and delicately curved ; its thickest 

 part lies just external to the body of the hyoid. The notches 

 in the hyoglossal sinus have disappeared, so that it is now 

 impossible to define the limits of the posteror copula and the 

 ceratohyal cartilage. The pointed lateral process of the hypo- 

 branchial plate is no longer distinguishable as such, but has 

 broadened out into a plate. The antero-lateral {pal) and postero- 

 lateral {ppl) processes are already disposed as in the adult. 

 Both are evidently secondary outgrowths, as Gaupp (3. p. 433 (4)) 

 has already shown to be the case in Bana. The antero-lateral 

 process is probably formed in great measure by the independent 

 cartilages (c, tig. 6), which remained free until the present stage. 



Stage 8. Adult specimen measuring 33 mm, from snout to cloam. 

 Length of hind limfj, extended, 46 mm. Length of fore limb, exteiided, 

 20 mm. (Plate 11. fig. 8.) 



It is surprising how slight are the differences between the hyo- 

 branchial skeleton of the just metamorphosed animal and that of 

 the fully-grown adult. The hyoglossal sinus has deepened con- 

 siderably, so that it is now behind the antero-lateral sinuses, 

 instead of being at the same transverse level with them as in 

 Stage 7. The broadest part of the ceratohyal lies, as in Stage 7, 

 just off the antero-lateral process. The ventral splint-bone is 

 completely ossified, but the ossification does not extend into the 

 subjacent cartilage. The bone is quite superficial, and can readily 

 be dissected off. The thyrohyals are well ossified, the posterior 

 extremities remaining cartilaginous and boot-shaped. 



SUMMAEY. 



In the hyobranchial skeleton of the early larva of Alytts there 

 is an anterior copula which subsequently disappears and forms no 

 part of the adult hyoid. 



The posterior copula extends backward to the laryngeal sinus, 

 and thus completely separates the two hypobranchia! plates. It 

 persists as the central part of the body of the hyoid. 



The postero-lateral process of the adult hyoid cannot be identified 

 with the base of the first ceratobranchial as it can in Pelodytes, 

 but both the antero-lateral and postero-lateral processes are new 

 formations, as in Bana. 



The branchial bars or ceratobranchials of the larva form no 

 part of the adult hyoid, but are entirely resorbed. 



The thyrohyal is developed from that part of the hypobranchial 

 cartilage of the larva which constitutes the inner boundary of the 

 thyroid foramen. 



List of Authokities befeeebd to. 



(A more complete bibliography on the Hyobranchial Skeleton of 

 Anura will be found in papers 8 and 9 of the following list.) 



1. Cope, E. D. — " Batrachia of North America." Bull. United 

 States National Museum, No. 34, 1889. 



