DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 59 



Tlie supra-stapedial is a secondary process of the distal part, and very inconstant ; 

 the segmentation of the extra-stapedial from the medio-stapedial is complete in 

 R. pcduslris and R. halecina (Plate 5), and I doubt not is the same for a time in 

 R. pipiens* 



The mandible in this species is chiefly remarkable for its great length (Plate 8, 

 fig. 3). All its parts are normal; the coronoid process of the "articulare" is well 

 developed. 



The hyo-branchial plate (Plate 8, fig. 5) is also quite normal ; it differs very slightly 

 indeed from that of the Common Frog, and as in that kind the stylo-hyal end of the 

 hyoid articulates with the floor of the tympanic cavity. 



As compared with the skuU of the "norma" we have many differences that are due 

 to their size, such as the distance of the facial bars, laterally, from the nasal labyrinth, 

 the small size of Llie cranial trough, and the huge suborbital spaces. 



The endocranium is not so much hardened as might be expected in so large a kind ; 

 the bony masses behind are still distinct below, but not in the superoccipital region. 



The investing bones generally are quite normal ; the roof in the parietal region has 

 its two sides anchylosed and crested : this is simply due to the extent and strength of 

 the temporal muscles. 



The cartilaginous foundations of the great palato-suspensorial arches is quite normal, 

 only they are very large, relatively. 



There are two groups of modified parts, namely, the various bony "centres" and the 

 elements of the middle ear. The modifications may be classified as follows : — 



1. Groups of small ossicles in a generalised state below the junction of the pre- 

 maxillaries and maxillaries, instead of a functional sejito-maxillary. 



2. Ectosteal bones apphed to the "palato-suspensorial arch" numerous, and in the 

 palatine region unsymmetrical ; several of those in the pterygoid region being refei-able 

 to normal iclithyic centres. 



.3. Further additions of bony centres in the pedicle and quadrate, both membrane- 

 hones and endosteal patches. 



4. The quadrate region of the suspensorium fenestrate, below the division into 

 "pedicle" and " otic process." 



5. A suh- and a pre-ovhitiH bone on each side. 



6. Parietal region anchylosed and crested. 



7. A distinct joro-parasphenoid. 



8. Inter-stapedial semi- osseous. 



9. Extra-stapedial half osseous, with distinct, but apposed, ectosteal and endosteal 

 tracts. 



10. Supra-stapedial confluent above. 



• This Acipenserine subdivision of the epi-liyal eleraent is to be seen also in the embryo of Cliehne 

 viridis. — "On the Skull of Chelune viridis," 'Challenger Memoirs.' ("Zoology," vol. i., part 5, plate 10, 

 tig 8, 1880.) 



