112 
ME. W. K. PABKEE ON THE STEUCTUEE AND 
This dropped semi-arch, thus suspended, is very large, and carries the infero-internal 
gill-cover fold, the branchiostegal membrane with its many parosteal rays. The main 
arch has an arcuate outline within, is flat above and knobbed below ; but this knobbed 
part, from the Sturgeon upwards, is segmented off, is cupped to fit to the convex end 
from which it has been taken, but there is no joint-cavity ; this distal part has two bony 
centres, and the upper third of the main arch has a centre distant from the rest of the 
bar. From above downwards “ epihyal,” “ ceratohyal,” and hypohyal; these may be 
the names, for the distal piece answers to the “ hypobranchials,” and not to their azygous 
keystone ; it has its own keystone, the “ glossal,” or rather “ basihyal,” a thick flattened 
bar, covered at top, sides, and end with a dentigerous ectosteal plate (Plate VI. fig. 1, 
and Plate VIII. fig. 9, ep>.h., c.hy ., h.hy., g.h.). These huge “ cornua” are strongly tied 
to the sides of the basal piece, near its end, and the first “ basibranchial ” runs up to the 
converging bars (Plate VIII. fig. 9, b.br.). 
The smaller arches, much smaller from the first in this high type, are devoted to 
respiration, all save the last, and are seen from their inner side (Plate VIII. fig. 9, br.) ; 
they are a regular series, decreasing, however, in size and specialization from before 
backwards ; they pass below within the hyoid arch, as it passes within the mandibular, 
telescopically. Each bar is normally segmented transversely into four cartilages, con- 
joined by a strong, short, fibrous ligament, and each of these has its own ectosteal sheath. 
The fourth arch has its upper piece unossified, and wants the distal segment ; the fifth is 
still more aborted, having a small separate upper cartilage and a larger lower piece 
which is ossified ; this arch is dentigerous and abranchiate, and is called the “ inferior 
pharyngeal.” The normal arches have their segments called “ pharyngo-,” “ epi-,” 
“ cerato-,” and “ hypobranchial,” and the keystone pieces are the basibranchials ; there 
is only one for the fourth and fifth arches, and it is unossified and segmented from the 
bar in front ; the three foremost have coalesced. These arches tend to fork above ; the 
first segment sends off a sort of pedate process (Plate VIII. fig. 9 , jj.br.), the next has its 
upper segment bifurcate, and also the next, the third articulates with the fourth and 
sends a fork from its “epibranchial” segment, the fourth sends out an epibranchial lobe, 
somewhat 3-lobed itself, and the fifth is simple. The third basibranchial (Plate VIII. 
fig. 9, b.br. s) is clamped on each side by a descending process of the corresponding 
“ hypobranchial,” and it sends downwards a cartilaginous hook from its lower end ; 
these are for muscular attachment. 
First Stage. — Salmon-embryos , before hatching , with the facial arches simple. 
V ith such specimens before him as those from which the following descriptions have 
been taken, it is not a little difficult for the worker to keep himself from wandering 
into general Embryology. 
This snare will, however, be avoided as much as possible, reference to the general 
bearing and relation of parts being made just enough to make the matter clear to the 
reader. As an introduction to this starting-ground, the inquirer will do well to read the 
