Page 681. 
348 ON THE ANATOMY OF PLOTUS LEVAILLANTI. 
margins of the gland areas, and has a small pit in the part corre- 
sponding to the surface between the limbs of the U, apparently not 
glandular in nature, All these structures are covered -with the tough 
gastric epithelium, which ceases just above them. 
The first true gastric cavity is larger than the second, though not 
much so, In the second the peculiar hairy covering of its pyloric 
portion is largely developed, and in a different manner from what it is 
in P. anhinga, where, as I have shown in my paper on the anatomy of 
that bird, it forms a kind of sieve to prevent large solid particles from 
entering the duodenum. In P. J/evaillanti a more elaborate arrange- 
ment obtains; the hairy epithelium surrounding the pyloric orifice, 
near the lower margin of the gastric surface of which it is developed, 
is produced into a considerable conical hair-covered process, projecting 
into the second stomach, and evidently acting as a valve to close the 
pylorus when necessary. In general appearance it much resembles 
the operculum of the Cheilostomatous Polyzoa, and is very striking 
at first sight, the hirsute conical plug when retracted, fitting exactly 
into the equally hirsute conical pyloric end of the second stomach- 
cavity. All the rest of the second stomach is lined with a non-hirsute 
epithelium, which ceases abruptly where it meets the hairy surface. I 
can find no trace of this operculum in Plotus anhinga, upon re- 
examination. 
The small intestine measured two feet, and the large three inches ; 
but they may have been contracted by the inflammation of their 
surfaces. Two minute ceca were clearly seen, one a little larger 
than the other. In P. anhinga there is no indication of a second 
cecum. 
As in P. anhinga, P. levaillanti possesses but one carotid artery, 
the left. In their myology the two species agree in every respect, 
as far as I can see. In P. levaillanti the ambiens is large, grooving 
the patella, the femoro-caudal is present without an accessorius, as 
is the semitendinosus. There is a slip from the biceps of the arm, 
which traverses the patagium; and the temporal muscles run back 
beyond the skull, being separated by a median fibrous raphé, which is 
not ossified into a separate bony style. The great pectoral muscle is 
formed of two layers. 
Donitz’s bridge is ossified, as in the specimen described by the 
author after whom it is named: it is developed on the ninth, and not 
on the eighth cervical vertebra, as I predicted would be the case. 
The lower larynx is indistinguishable from that of P. anhinga. 
It is interesting to notice that the Manatee and Dugong have 
special gastric gland-structures, the method of arrangement of which 
differs in exactly the same way as does that of the two species of 
Plotus under consideration, the peculiar flat gland-area found in 
