OF THE SKULL IN LEPIDOSTEUS OSSEUS. 
451 
roughly scythe-shaped, the “ blade ” being behind, and lying between the auditory cap¬ 
sule and the narrowing basal band, whilst the “handle” is in front, and is glued to the 
trabecula. The blade is shorter than the handle, and on its heel it has an oval, condyloid 
facet, which looks forwards and a little outwards and downwards ; it is pinched a little 
behind this facet, and then becomes an apiculated lanceolate blade. The handle is oval 
in section, narrow at first, and then wider as it turns inwards at its junction with the 
trabecula. A free bar, rather shorter than the “ handle,” and having its thick end 
reversed, or behind, articulates by a flat facet with the flat facet of the suspensorium. 
This is Meckel’s cartilage, or the free mandible ( mk.). 
Already, in the coronoid region, this short lower jaw is elevated into a crest; its lower 
edge is convex, its upper concave, and its end is blunt; it reaches nearly as far forwards 
as the palatine region of the suspensorium. Between the convex hind margin of the 
first arch (suspensorium and mandible) and the concave fore margin of the next (the 
hyoid) arch there is a hypoblastic pouch (see Plate 30, figs. 1 and 2, cl 1 .), but this first 
cleft does not open on the outside, like the hyo-branchial and four branchials. ■ 
The hyoid arch consists already of four segments on each side, with the rudiment 
of a median conjugating bar, composed of embryonic cartilage. The pier (Jim.) of the 
hyoid arch, like its counterpart in the Mammal, is anvil-shaped ; this is the hyo- 
mandibular, with its symplectic process, the counterpart of the pterygoid fore-growth 
of the mandibular pier or suspensorium. * 
At present it is only a fourth less than the pier in front of it; but it becomes 
relatively much less, instead of much larger, as in the Teleostei. The hyomandibular is 
now a solid mass of cartilage, concave above, bilobate below, and sending upwards, to 
the auditory capsule, a thick process, and downwards, to the articular process of the 
suspensorium, a sharp process. The upper process is its proximal part or head, the 
lower is its symplectic prolongation. 
The middle part has two lobes, below, and behind ; the upper of these afterwards 
gives off the opercular process, the lower is already scooped on its inside where it 
articulates with the next joint, the inter-hyal ( i.hy .). This latter piece is a small 
pyriform segment, with its lesser end upwards and hooked inwards, for articulation 
with the hyomandibular. This is, so to speak, a supernumerary segment placed 
between the antero-superior pier and the postero-inferior arch. That arch is already 
composed of a main bar above, the cerato-hyal (< c.hy .),—a thick rounded rod, and a short, 
almost globular segment below, the hypo-hyal (, h.hy .); the two fit together by flat facets ; 
the right and left hypo-hyals touch each other below. In front of and between these 
lower segments there is a tract of tissue which will harden into the basi-hyal ( b.hyf 
The branchial arches (br.) are slender rods, bent in a sigmoid manner so as to form 
round in-turned hooks, above. The last (br 5 .) is only one-fourth as large as the other 
* Mr. Balfour informs me that this bar is primarily continuous with the skull, and that after chondri- 
fication it is still unsegmented. 
