DEVELOPMENT OF THE SKULL IN THE BATRACHIA. 
251 
near the remarkable modifications seen in Pipa (ibid., Plate 62, figs. 2 and 9, sq.) ; in 
that strange type the outer and middle ear meet in, and cover, a curious spoon-shaped 
process of the squamosal. 
The parasphenoid (fig. 2, pens.) is evidently large, but its boundaries are very indis¬ 
tinct through anchylosis; it has between its three main rays a rather rare “ apophysis;” 
this is a transverse, rounded projection, looking forwards, and downwards; it has a 
hollow in front of it, and a mammillate elevation behind. 
There is not a trace of the right and left vomer ; in this, again, we see a character 
in which this type agrees with Pipa. 
But Hylaplesia agrees in some important characters with the other Aglossal type, 
viz. : Dactyletlira (Phil. Trans., 1876, Plate 59). This similarity is to be seen in the 
Salamandrian extension of bone in the endocranium ; in the superior aspect of the 
occipital condyles—not to the same extent, but as much seen above as below; in the 
huge size of the “middle ear,” and especially its inter- and extra-stapedial elements. 
I look upon these similarities rather as an expression of the generalised nature of both 
kinds than as suggesting genetic relationships. 
With the adopted and natural “ norma” the skull of Hylaplesia presents remarkable 
contrasts ; they may be summed up as follows :— 
1. The general form of the skull is as much longer than what is typical, as that 
of Callula is shorter. 
2. The great breadth and strength of the cranium as compared with the feebleness 
of the face. 
3. The arrested retreat of the quadrates and their condyles. 
4. The extreme breadth of the muzzle. 
5. The intense ossification of the endocranium, and the anchylosis with it of the 
investing bones. 
6. The absence of vomers. 
7. The apophysis on the parasphenoid. 
8. The superior as well as inferior aspect of the occipital condyles. 
9. The small size of the tympano-Eustachian cavity, and the increase of room in 
that “ cleft” by the hollowing out of the squamosal, above. 
10. The very open annulus and large stapes. 
11. The huge size, relatively, of the columella, and especially of its proximal and 
distal elements. 
12. The large size of the three pairs of labials—the lower as mento-Meckelians. 
13. The presence of a considerable pre-orbital besides the septo-maxillary. 
14. The reversed position of the hypo-hyal lobe, the smallness of the basal plate, 
and large size of the thyro-hyals. 
These are some of the more outstanding peculiarities of this strong little skull, whose 
generalised nature is shown, also, in its unlooked-for agreement with the archaic and 
non-typical skulls of the “ Aglossa.” 
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