22 
MR. W. K. PARKER ON THE STRUCTURE AND 
parietals ( f.p .), thin wedge-shaped shells of bone on the roof; and the parasphenoid 
( pa.s .), a large dagger-shaped bone lying under the floor; its point is rounded and the 
median hind process is a low triangle ; the “ basi-temporal wings ” are broad and oblique 
at their outer end. 
These three are subcutaneous ossifications, but there is also a series of subcutaneous 
cartilages. 
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The suctorial mouth is mainly formed by a coalesced upper pair and a distinct lower 
pair of these, here called “labials” ( u.l., I.I.). 
The upper piece shows where it was once in two distinct parts ; it is a broad 
crescentic arched flap, with outer angles, an emarginate hind, and a round front, margin. 
Towards the sides there is a small fenestra, which is the beginning of a new sub¬ 
division ; the angles answer to the upper angular cartilages of the Lamprey’s mouth, 
and the main part to the “anterior dorsal cartilage” of that Fish. The “ lower labials” 
form together a horseshoe, and are fixed in between the mandibles; they have a 
thick lower edge and a concave inner face (fig. 2, l.l.). 
The wedge-shaped ray of cartilage, which is confluent with the “tegmen tympani,” 
and articulates with the otic angle of the suspensorium, answers to the mandibular ray 
(the “ spiracular cartilage)” of the Shark: it becomes the “annulus.” The extra- 
branchials will be described in the next instance; part of the first (ex.br 1 .) is shown 
in fig. 7. 
Second Stage. —2 . Tadpoles of Lana pipiens (A and B), from 3§ inches to 5 inches 
long, with hind legs appearing. 
In the largest of these I shall show the details of the structure of the palate, 
mouth, and throat (Plate 1, figs. 3-5); and in the lesser specimens the skull and 
face (Plate 3, figs. 1-3). 
On the whole, the structure of the chondrocranium is very similar to that just 
described; there are, however, some very instructive differences. 
The skull (Plate 3, figs. 1-3) is altogether rounder, less angular, and free from the 
projecting snags; the occipital arch is wider and flatter, the cranial cavity not so 
oblong, but is pinched in in the middle. The internal nostrils ( i.n.) are oblique and 
subi’eniform, converging towards each other behind; thus the palato-pterygoid bar 
( p.pg .) is longer and more oblique, and its post-palatine rudiment (pt.pa.) projects less 
into the larger and more oval subocular space. The cornua trabeculae ( c.tr .) have 
wider ends and with a more pronounced outer angle, the outer wings of the ethmoid 
(al.e.) are not so well developed, and the vertical septum ( p.e .) is shorter. 
In the side walls (fig. 3) the cartilage is low, and the hinder roof-cartilage (“ tegmen 
cranii”), with its two fontanelles, is seen to grow forwards from behind, and not to 
be continuous with the low side wall. 
In this stage, even, besides the centres of bone that grow inside the 9th and 10th 
nerves (e.o., IX., X.), there is on each side a bony patch in front of the ear-capsules ; 
