Prof. Owen's Description of the Lepidosiren annectens. 341 
the transmission of the acoustic nerve“. This nerve divides almost immedi- 
ately into two branches, one of which is distributed over the sac of the lesser 
otolithef, and sends a branch to the semicircular canals; the other is ex- 
pended upon the sac of the greater otolithet. These sacs occupy the inferior 
part of the vestibule; the smaller one is internal, and about one sixth the size 
of the outer sac; both are of a spherical form, and are nearly filled with a white 
chalky substance, which here, as in the Cartilaginous Fishes, represents the 
hard otolithes of the Osseous Fishes. Above these sacs are three small semi- 
circular canals$. There is not a vestige of tympanic cavity or Eustachian tube. 
Of the fifth pair of nerves only the second and third divisions are present |. 
The eighth pair of nerves supplies the branchial apparatus, sends a branch 
along the pharynx to the alimentary canal and air-sacs, and terminates in a 
large lateral nerve, which is continued backwards over the heads of the ribs 
to the middle of the caudal region, where it distributes its terminal branches 
to the muscles of the natatory membrane. 
There is no modification worthy of notice, as bearing on the affinities of the 
Lepidosiren, in the spinal chord or nerves. 
Digestive System. 
The mouth is of moderate width, and is provided with fleshy lips, behind 
which are the papillose processes already described, and which are doubtless 
organs of delicate touch: the dental apparatus consists of the two long, move- 
able, piercing teeth descending from the intermaxillary bone, and the strong 
trenchant and crushing dental plates which incase the opposed margins of the 
upper and lower jaws. 
Immediately behind the dental plate of the upper jaw there is a broad pro- 
cess of the palatal membrane beset with minute papillæ**, which it may be 
allowable, perhaps, to compare with the minute palatal teeth of the Siren, here 
represented in their uncalcified rudimental state. Behind the lower jaw there 
is a smooth transverse duplicature of the membrane of the mouth, covering 
the anterior extremities of the cerato-hyoids: this process is succeeded by a 
second trilobate, narrow, transverse fold tt, minutely papillose and glandular. 
* Tan. XXVII. fig. 4, k. t Ib. fig. 4,1. t Ib. fig. 4, m. $ Ib. fig. 3, n. 
| Ib. fig. 4, o. € Ib. fig. 2. * Tas. XXIV. fig. 2, g. tt Tas. XXVI. fig. 1, b. 
