22 MR. W. K. PARKER ON THE STRUCTURE AND 



parietaJs {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. 



The suctorial mouth is mainly formed by a coalesced upper pair and a distinct lower 

 pair of tliese, 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 emarglnate 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, /./.). 



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.hr^.) is shown 

 in fig. 7. 



Second Stage. — 2. Tadpoles of Rana pipiens (A and B), from 3f inches to 5 inches 



long, with Jiind 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 

 subreniform, converging towards each other behind; thus the palato-pterygoid bar 

 {p-P9-) is longer and more oblique, and its post-palatine rudiment {2}t.pa.) projects less 

 into the larger and more oval subocular space. The cornua trabeculse (ctr.) have 

 wider ends and with a more pronounced outer angle, the outer wings of the ethmoid 

 {cd.e.) are not so well developed, and the vertical septum {jJ-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 1 0th 

 nerves {e.o., IX., X.), there is on each side a bony patch in front of the ear-capsules ; 



