336 Prof. Owzw's Description of the Lepidosiren annectens. 
sponding central groove and lateral ridges in the concave articular surface of 
the lower jaw. Moreover, this double articular trochlea is not bony but car- 
tilaginous in both the pedicle aud the lower jaw. "The convex or upper part 
of the joint forms the termination of an elongated piece of cartilage continued 
from that which represents the squamo-temporal bone, downwards and for- 
wards, between the expanded end of the pterygoid plate above-described, 
which forms its internal support, and an elongated plate of bone, which runs 
parallel with the cartilaginous pedicle and adheres to its outer side. This 
outer plate of bone may be regarded as a rudimental os tympanicum* : its 
inferior extremity is regularly convex, and forms the outer edge of the man- 
dibular articulation: above this part it becomes contracted, and, as it were, 
twisted, with the posterior edge turned outwards, so as to render its external 
surface concave; it then again becomes expanded and compressed, as it as- 
cends obliquely backwards and terminates in a rounded edge, which gradually 
degenerates into cartilage. 
Each ramus of the lower jaw is composed of an articular or post-mandibu- 
lar t and a dentary piece, as in most osseous fishes. The articular piece is an 
elongated compressed bone, concave posteriorly where it forms the outer mar- 
gin of the articular surface, and extending forwards in a groove on the outer 
and near the lower part of the dentary piece; it ends in a point near the sym- 
physis. The cartilage, which forms the principal part of the articular conca- 
vity, extends forwards on the inner side of the postmandibular bone half-way 
towards the symphysis. The dentary elements are anchylosed to each other 
at the symphysis, and each is deeply notched behind for the reception of the 
apes a the postmandibular bone. Their masticating or upper surface is mo- 
dified in correspondence with the dental surface of the opposed jaw; three 
= pont Ped A the anterior being like that in the 
; and with the external angle most pointed 
earing ; the posterior one is the thin- 
nest, and best fitted for cutting : 5 
