OF THE SKULL IN LEPIDOSTEUS OSSEUS. 
485 
quadrate. As in the Tadpole, the fore end of this bar is fixed; as in the Teleostean 
Urodele, and adult Frog, the hind part, or pedicle, is free. 
As in the Tadpole, the suspensorium is sub-parallel with the axis of the skull, and 
the free mandible (Meckel’s cartilage) grows forwards and inwards ; that condition is 
temporary in the Batrachian, it is permanent in Lepidosteus. 
As to the development of the basal bands of the skull, this type agrees with the 
Selachians and Teleosteans ( Salmo ) in the synchronism of the para- and pro- chordal 
tracts ; but in Batrachians, Urodeles, and Marsipobranchs, the trabeculce are developed 
first; they embrace the fore end of the notochord closely, and are both para- and 
pro-chordal; afterwards the hinder parachordal region is chondrified, separately in 
Urodeles, and continuously in Batrachians and Marsipobranchs. 
The development of the complex hyoid arch is very different in this Holostean 
Ganoid, and in the Chondrostean Sturgeon, from what we find in Teleosteans, 
Batrachians, and Urodeles. 
In the Salmon the primary bar breaks up into two long bands, with a short segment 
below ; the foremost is the larger, retains its connexion with the ear-capsule, widens 
above as the hyomandibular, and narrows, antero-inferiorly, as the symplectic region. 
The narrower, hind band becomes postero-inferior in position, keeps the small distal 
segment, and acquires a new, small segment, above, by which it becomes attached to 
the space between the hyomandibular and symplectic ; the late, small upper segment 
is the inter-hyal, the long bar the epi-ceratohyal, and the short, distal segment the 
hypo-hyal. 
In the lowest Urodele, Proteus, the hyoid arch is composed of two massive segments, 
one short, the upper or hyomandibular, and the other, the long, lower bar, the cerato- 
hyal; this is like that which obtains in Shanks. 
In the larger Urodeles ( Menopoma, Cryptobranchus ) there is but little difference 
(apparently) in the time of development of the segments, but the upper part breaks 
up into two segments corresponding to the hyomandibular and symplectic segments in 
the Sturgeon ; the cerato-hyal is large, and the hypo-hyal breaks up into three pieces. 
In many of the Caducibranchiate Urodeles, and in some kinds of Anura (Sala- 
mandra, Triton, Pseudophryne, Bombinator), all but tbe uppermost part of the hyoid 
arch is suppressed ; but in the Batrachia, generally, it is developed, as two, three, or 
even four segments; these, with the exception of the uppermost, as a rule, do not 
appear until two or three months after transformation, and are only developed in 
the Tadpole in rare cases, as in Pseudis and Pipa. 
In Lepidosteus and in Acipenser the formation of the segments of the hyoid arch 
takes place at once during chondrification; Lepidosteus has the same number of carti¬ 
lages as the Teleostei, but Acipenser has a distinct symplectic piece—a kind of 
segmentation which is not equivalent to the subdivision of the upper part of a 
branchial arch into a pharyngo- and an epz’-branchial, but the epi-hyal is segmented 
at its distal fourth. 
