THE OSTEOLOGY OF AMIURUS CATUS. 287 
and the posterior extremity of the ethmo-palatine cartilages. Whether 
this is really so my specimens do not allow of absolute certainty, but 
make it a strong probability. Somewhat further back the cartilage 
is seen and may be traced unbroken back to the quadrate. .The 
metapterygoid of Amzwrws combines to a certain extent the relations 
of the ectopterygoid and entopterygoid, as well as that of the metap- 
terygoid of other Teleosts, but, since it is in direct relation to the 
quadrate, and performs the usual function of a buttress to the hyom- 
andibular, I have preterred the last named term for it. 
The development of the dentary suggests some important thoughts. 
In a 20 mm. stage, (Fig. 9) Meckel’s cartilage Mck) is present in its 
entirety. On its upper surface is a layer of tooth-bearing bone, in 
which the individual cement plates (cp) are still to a large extent re- 
cognizable. At the sides and below is a layer of perichondral bone 
(pe), the cement plate bone passing into it without any line of demar- 
cation. In fact both varieties are identical, not only in their histolo- 
gical features, but also in their origin. Below the cartilage is a 
mucous canal (MC) enclosed in its osseous tube, which is united with 
the perichondral bone of the lower surface. In a 38 mm. stage the 
cartilage has almost disappeared, its place being occupied by trabecu- 
lx of bone, osteoblasts lying in the interspaces. The mucous bone 
has become quite united with these trabecule, and it is impossible to 
distinguish it. We have then in the dentary portion of the man- 
dible what may be termed three different varieties of bowe—cement- 
bone, perichondral-bone (with which may be included the trabeculz), 
and mucous-canal bone. All three, however, pass into each other, 
and are indistinguishable in structure and origin. The old division 
into primary and secondary ossification should be done away with 
since both varieties are in reality similar. 
Ill.—_THE HYOMANDIBULAR, HYOID, AND OPERCULAR 
APPARATUS. 
The bones constituting these parts belong to a single arch, the 
second post-oral, and are in relation to the seventh nerve. 
1. Tue Hyomanpisurar, (PI. II., Fig. 1, Hid.) 
Is a large almost quadrate bone, forming the upper part of the 
arch. It articulates above by a somewhat arched surface with the 
sphenotic and pterotic, and from the anterior angle of this surface a 
