346 Prof. OweEn’s Description of the Lepidosiren annectens. 
and third branchial arches; and the corresponding arterial trunks* undergo 
no subdivision as they wind round them, but are continued entire, as in the 
Amphiuma and Menopoma, to their termination at the opposite side of the vas- 
cular circle. The branches which afterwards unite to form the single pulmo- 
nary artery on each side are given off from near the termination of the se- 
cond and third pairs of the primitive aortic trunk ; which thus combine the 
functions of both systemic and pulmonary arteries. 
The branchiz of the Lepidosiren resemble in form those of the Siren, con- 
sisting of separate elongated filaments, attached only by one extremity to the 
branchial arch ; but these extremities are fixed directly to the branchial arch, 
and not to a common pedicle extended therefrom, as in the Siven. Viewed 
with a moderate lens the tripinnatifid structure is beautifully seen in each 
branchial filament. The first gillt consists of a single row of fourteen of these 
subcompressed filaments, each of which is about one line in length and a 
third of a line in breadth. "The second gillt, which is developed, as before 
stated, on the fourth branchial arch, is the largest, and consists of a double 
row of fifteen branchial filaments. The third gill$ has a similar structure. 
The fourth gill || consists, like the first, of a single row of fourteen tripinnatifid 
filaments, which are shorter and smaller than those of the first. 
The cartilaginous branchial arches are developed on each side in the sub- 
mucous tissue, and, as before stated, are not attached either to the. hyoid ap- 
paratus below, or to the cranium above. The membrane covering the 3rd, 
4th, and 5th arches is minutely papillose. The first branchial aperture or 
interspace is a narrow slit three lines long, and is defended by a series of 
minute denticulations projecting from the branchial arch. Bristles are repre- 
sented as passing through the five branchial interspaces in Tak. XXV. fig. 3. 
The second aperture** is the widest; it is five lines long, and its margins are 
smooth: the third aperture is also five lines long, 
second: small cartilaginous teeth are developed fro 
in the first gill-aperture: the fourth and fifth a 
structure but diminish in size. 
but is narrower than the 
m each of its margins, as 
pertures present the same 
Thus the branchial current, which flows through the interspaces of those 
Tan. XXVI. fig. 2, 2 K 3. + Ib. fig. 2, 1. t Ib. fig. 2, 4. § Ib. fig. 2, 5 
Ib. fig. 2, 6. € Ib. fig. 1, 1. ** Tb. fig. 1, 9. 
