194 
ME. W. K. PAEKEE ON THE STETTCTUEE AND 
So much, at any rate, maybe said of the skull and face of the Lamprey as read in the 
light of the development of the same parts in the Frog ; they mutually illustrate each 
other ; and in my ten stages, whilst the earliest is two steps lower than the Ammoccetine 
larva, as given by Muller, yet, if the oldest stage of the Frog’s skull (see Plate IX. 
figs. 6 & 7) be compared with that of the adult Lamprey, it is evident at once that, 
notwithstanding its almost mammalian metamorphosis of certain parts, much that is 
truly petromyzine 'remains in the old Frog. 
2. With the Skull of Chimtera. — The skull and face of this remarkable type may be 
illustrated by the earliest conditions of those of the Tadpole. 
In the Chimseroids the excessive growth of cartilage (Muller, op. cit. ; Huxlet, 
Elem. pp. 195-197, figs. 77, 78) has obliterated all traces of distinction between the 
“ investing mass,” “ trabeculse,” a large part of the first and second postoral arches, and 
the auditory capsules. 
The space formed by divergence of the trabecular and mandibular bars is entirely 
filled in by cartilage, so that the “orbitar process” is not a distinct flap from the pterygo- 
palatine; and the “subocular fenestra” is also completely occupied by the same growth. 
Thus there is no distinction between the “metapterygoid” and “mesopterygoid” regions 
(Huxley, fig. 78, D); and there is no boundary between the prefrontal and palatal 
regions. The “trabecula rhorns” are thoroughly involved in the nasal walls; but they 
send out symmetrical and also single outgrowths as “ snout-cartilages” (Muller, op. cit. 
pi. 5, fig. 2, i, h). The mandibular arch also developes an outgrowth below as in the 
Lamprey ; but this is segmented off as in the Frog : this thick mass of cartilage (C) is 
“ Meckel’s rod.” The third (hyoid) arch is largely confluent with the second ; but in 
Huxley’s figure of Chimcera monstrosa a groove is shown on the inner side (fig. 7 8) ; 
this is the remnant of the upper half of the first postoral cleft ; yet the parts before and 
behind it, the metapterygoid and hyo-mandibular regions, are thoroughly confluent. As 
in the Lamprey and Frog, the lower diverging half becomes segmented off from the 
second postoral as the liyoidean apparatus (Muller, fig. 2, kfm; Huxley, fig. 77, o). 
There are many upper and lateral “ labials ;” but there is a large single horseshoe-shaped 
lower piece (Muller, c ). 
The trabecular floor of the skull (Huxley, fig. 78) is thin; and from the commissural 
region there proceeds a transverse wall separating the cranial from the nasal cavity, 
exactly as in the Tadpole. 
The great “upper fontanel! e” is entirely roofed-in with solid cartilage, which is con- 
tinuous with the shelving nasal roof (No) : thus in Chimcera we have middle and lateral 
ethmoids, with their upper alar growths all marked out, and also the Batrachian trabe- 
cular floor. 
3. With the Skull of Sharks and Mays. — In Squatina (Muller, op. cit. pi. 5. figs. 5, 6 ; 
Huxley, Elem. p. 198, figs. 79, 80) the trabecuke are entirely involved in the skull 
and nasal sacs, so that the front part is short and transverse as in the Frog. The labial 
plate was broken up into two rays on each side above, and one below. But the things 
