44S 
MR. W. K. PARKER OK THE SKELETON 
forwards , above and below it. The first bar encloses its aperture by a simple loop of 
cartilage; in the skin in front of this loop we see the fore end of the branchial groove, 
in which place I have, many a time, searched in vain for the ls£ cleft, the hyomandi- 
bular ; the first open passage is the hyobranchial, and thus the fore half of the first 
branchial pouch must be accredited to the hyoid region. In the Tadpole the hyoid has 
no gill, and its three clefts answer to the second, third, and fourth of the Lamprey; 
the former has three pouches, four extra-branchials, and four rudimentary cerato- 
branchials inside, which form an imperfect fringed floor or septum between the food- 
pharynx and the respiratory cavities (see Phil. Trans., 1881, Plate 1, fig. 4). 
D.— V 'ertically-transverse sections of the head and branchial region of a 
large (but not ripe) larva of P. fluviatilis. 
ls£ Section (Plate 19, fig. G).—The first of these sections (see also Plate 8, figs. 4-6) 
is through the external nasal opening (e.n.), and the upper lip ( u.lp.) with its 
undergrowth of mass-like barbels ( bb .) ; the bps are of great depth, and the top of 
the face is concave. 
2nd Section (Plate 19, fig. 7).—In this the nasal roof ( na .) is cut across behind 
the opening. The top of the face is still more concave than in the last, and the whole 
section is deeper. 
3rd Section (Plate 26, fig. 1).—The roof (na.) of the nasal capsule is cut through 
here so as to miss the median part. The capsule is more vertical than could be shown 
in the dissections (Plate 19, figs. 4, 5, na.), and the bilobate organ of smell ( ol.) 
is laid bare; the other parts are similar to what is seen in the last. 
4 th Section (partial; Plate 26, fig. 2).-—Here the hinder angles of the capsule (na.) 
are cut across, and the olfactory lobes (C 1/j .) are seen in section ; barbels are still seen 
under the hood-like upper lip. The fore part of the nasal canal (; p.n.c .) is shown. 
5 th Section (partial; Plate 26, fig. 3).—This is very similar to the last, but further 
back: this shows the angles of the nasal cartilage (na.) for the last time, and the 
large olfactory crura (C 1/ '.) are cut across their middle. 
6th Section (partial; Plate 26, fig. 4).—The fore brain (C 1 .) and pineal body (pul.) 
are here severed, and the skull in its front region; the section is through the fore 
part of the ethmoid (eth.), behind the nasal sacs; the barbels (bb.) of the upper lip 
(u.lp.) are becoming folds. The proximal part of the posterior nasal canal (p.n.c.) is 
circular at this point. 
7th Section (partial; Plate 26, fig. 5).—This is close behind the last, and shows the 
fore part of the cranial trough formed by the ethmoidal commissure of the trabeculae. 
The posterior nasal canal (p.n.c.) is now crescentic in section, with the concavity 
above. 
8 th Section (Plate 26, fig. 6).—Here the fore brain (C 1 .) rests upon the trabeculae 
