174 
MR W. K. PARKER OK THE STRUCTURE AUD 
The neck and shoulders of the hyomandibular are ossified, so as to leave the round 
convex head and expanded lower part unchanged. The osseous shaft is hour-glass¬ 
shaped, very thick, and leaving only a small core of cartilage unossified (Plate 18, 
figs. 5-7, hm.) ; this bony tract is very angular, in section, and somewhat four- 
cornered. On the outside of the bony sheath, embedded in the periosteum, there are 
simple and forked cartilages (Plate 18, figs. 5, 6, 7, hm.r.), evidently rudimentary 
“branchial-rays; ” as seen in the sections (figs. 6, 7) they are very solid, “and usually 
exist upon (a) the anterior, and (b) the outer face only; in one specimen, however, 
(fig. 7) they also occurred upon the anterior and inner” (Howes) ; they are very 
variable as these sections show. 
The “ toe ” of the hyomandibular (hm.) rests upon the upper face of the upper end 
of the next segment, the symplectic or lower epi-hyal (Plate 18, fig. 5, sy.) ; the two 
are attached together by a strong fibrous joint. This distal segment of the hyoid 
"pier” is half the length and half the medium width of the upper piece; it is 
phalangiform, straight, and thick. Distally it is attached by a strong fibrous joint to 
the quadrate region (q.c.), which it carries ; proximally, at its proper upper end it is 
articulated to the inter-hyal (i.hy.); it is wholly unossified. 
The intercalary segment, or “inter-hyal” (i.hy.) is a sub-cubical, lobulated mass of 
cartilage, interposed between the symplectic and the lower element of the hyoid arch, 
the cerato-hyal (c.hy.). This latter segment in the undisturbed condition of the 
parts runs across and a little forwards under the throat; it is about the size of the 
symplectic, but more slender and has a narrow waisted ectosteal tract a little below 
its middle. This bone is nearly half the height of the bar, is pinched and angular, 
has an unossified pith and extra-hyal cartilages (Plate 18, fig. 9, c.lvy., c.hy.r.), like the 
hyomandibular. 
There is a thick wedge of cartilage segmented off from the cerato-hyal, the hypo- 
hyal (h.hy.) ; it is attached by fibrous tissue to its fellow, the related ends being 
narrow, and also to the fore end of the first basi-branchial (Plate 18, figs. 5 and 
10, h.hy., b.br 1 .). 
The thick, solid, strongly bent branchial arches (Plate 18, figs. 5 and 10) lessen and 
become simpler from before backwards. The joint between the main mpper and 
lower segments (e.br., c.br.) is a well formed “ elbow,” the upper part is a little less 
than the lower. Only the first and second branchial arches are perfect, and they 
have acquired an additional pharyngo-branchial (fig. 5), and these small segments rest 
on short forks of the epi-branchial (e.br.). There is only one pharygno-branchial on 
the third arch ( p.br 3 .), and that on the fourth has (evidently) become fused with the 
epi-branchial (e.br\). The fifth arch is in one piece, it is a cerato-branchial (fig. 10, c.br 5 .), 
and like the four cerato-branchials in front of it, has a bony tract in its middle part. 
Only the first and second epi-branchials (e.br 1 ., e.br 2 .) have ectosteal tracts. On the first 
of these there are at least two imperfect “rays”' (br.r.), as on the arches in front. 
The lower part of each arch is bowed outwards, the upper is sigmoid, and they are very 
