NECTURUS MACULATUS. 493 
open gill slits guarded by rudiments of gill rakers, much as in the Axolotl, and as these 
occur, the one between the first and the second arches, and the other between the second 
and the third, and consequently in the intervals between the integumental branchiae, the 
suggestion of connection between the two systems is still more misleading. It may be 
remembered in this connection that there is a similar external gill upon the shoulder 
girdle in the Dipnoan, Protopterus, the relation of the two being wholly topographical 
and without morphological significance. Hence the physiological moments which have 
developed the external branchiae in this place are plainly the utilization of the gills and 
their muscular mechanism for support and motion, as well as the currents of fresh water 
which can be driven through the gill slits in such a way as to bathe the respiratory 
fringes. 
Since the attempt of Fischer (’64) to account for a fourth branchial arch by supposing 
that the first consists of two fused arches, no good suggestion concerning branchial arches 
posterior to the third had been made up to about ten years ago, since when a series of 
investigations by Gegenbaur (29’), Géppert (94), and myself (92), have rendered it 
probable that the laryngo-tracheal cartilages of Amphibia are modified portions of the 
fifth arch, perhaps the epibranchials. A fourth arch, attached to the hyobranchial 
apparatus, is present in several of the lower Urodeles, (Siren, Amphiuma, Crypto- 
branchus), and its apparent absence in Necturus has awakened some little speculation. 
The rudiment of this was finally discovered by Géppert, who found it to consist of a 
raphe of connective tissue, separating two muscles normally belonging to the branchial 
system, and in which, in the larva, he discovered a few cartilage cells. This view I can 
corroborate by investigations upon the same point at the same time, and which had led 
me independently to the same conclusions previous to the appearance of the work of 
Géppert. This raphe is given in the figure referred to (pl. 65, fig. 12), and there can now 
be little doubt that it represents the missing fourth epibranchial. Concerning the struc- 
ture of the metamorphosed fifth branchial arches (laryngo-tracheal cartilages), they con- 
sist normally of a single pair of somewhat curved pieces, applied to the sides of the glottis 
and short trachea, and were first described by Henle under the name of cartilago lateralis. 
They are individually very variable and often have notches, foramina, or detached pieces, 
but consist essentially of an anterior flat piece in the form of a triangle, from the poste- 
rior internal angle of which depends a curved tracheal process extending posteriorly. A 
more careful description of these cartilages and figures of several varying forms are given 
in the author’s article on the amphibian larynx (96). 
Suspensorial relations of the hyoid.— The distal end of the ceratohyal enters into a 
ligamentous connection with various parts of the skull and mandible and thus bears a 
close relation to the suspensorial apparatus of the mandible, a region which has such an 
