DEVELOPMENT OF THE SKULL IN THE J3ATRACHIA. 
59 
The 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. pcdustris 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 skull 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 the 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 septo-maxillary. 
2. Ectosteal bones applied to the “palato-suspensorial arch” numerous, and in the 
palatine region unsymmetrical; several of those in the pterygoid region being referable 
to normal ichthyic centres. 
3. Further additions of bony centres in the pedicle and quadrate, both membrane- 
bones and endosteal patches. 
4. The quadrate region of the suspensorium fenestrate, below the division into 
“pedicle” and “otic process.” 
5. A sub- and a pre-orbital bone on each side. 
6. Parietal region anchylosed and crested. 
7. A distinct pro-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 Adpenserine subdivision of the epi-hyal element is to be seen also in the embryo of Chelone 
viridis. —“ On the Skull of Chelone viridis ,” ‘ Challenger Memoirs.’ (“ Zoology,” vol. i., part 5, plate 10, 
fig 8, 1880.) 
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