bo 
20 MR. W. K. PARKER ON THE STRUCTURE AND DEVELOPMENT 
(the quadrate, g), has grown forwards, and has become a large upper jaw, the “ pterygo- 
quadrate ;” whilst the remainder of the primary stem hinges with the outturned end of 
this as the lower jaw—articulo-Meckelian (Pl. XL. figs. 4 & 5, g.pg, ar.mn). 
These two arches (¢wo by metamorphosis) in rest are but slightly bowed forwards, 
where they meet their fellow bars of the opposite side; they are almost directly trans- 
verse, and conform, as every thing else does, to the flat outspread form of this peculiar 
type of Fish. 
The second postoral (hyoid) was also forked above in the early embryo; the further 
development of that arch is similar to what takes place in the Teleostean (e.g. Salmon): 
but it is arrested at a lower morphological level. 
The anterior fork of the second postoral articulates with the auditory capsule beneath 
the pterotic ridge (“ tegmen tympani”) by an oblong condyle above (PI. XL. fig. 4, h.m), 
whilst below it becomes detached entirely from the rest of the bar, turns forwards close 
behind the spiracle, which it protects, as the metapterygoid does in front, and then 
fastens itself strongly by ligamentous fibres to the quadrate, becoming its new additional 
suspensorium. 
The hinder fork, or proper apex, is wholly freed from the hyo-mandibular ; its upper 
piece, or “ epihyal,” is in reality only half the epihyal region, having lost the hyo- 
mandibular wedge. Thus the expanded apex of the archis cleft obliquely, as in Saurop- 
sida and Mammalia, and not from top to bottom, as in Teleostei, nor simply across 
without subdivision of the ‘‘epihyal” region, as we have just seen in the Dog-fish. The 
bar, freed from the anterior fork, is now developed into a rather feeble branchial arch ; 
it is attached by ligament to the end of the jutting pterotic above; and the upper or 
epihyal segment is exactly like the epibranchials (Pl. XL. fig. 4, e.hy, ¢.br), save that it 
is smaller than most of them, and, being attached to the corner of the skull, sends 
no “ pharyngo-pleural” segment over the pharynx. There is no secondary cartilage 
developed in the attaching ligament, as in Teleostei; the “interhyal” (‘ stylohyal,” 
Cuy.) is fibrous. 
The ceratohyal (c.hy) is feeble, but normally branchial in character; the arch is 
finished below by a small styliform hypohyal segment; this is attached by ligament to 
the first hypobranchial (fig. 5, h.hy, h.br 1). 
Here we see a vast difference between the Shark and Skate ; for in the former the stout 
two-membered bars of the hyoid have their ventral ends strongly articulated to a large 
basihyal piece; whereas in the Skate the lower ends of the hyoid are nearly as far 
apart as the breadth of the transverse mouth. 
The five branchial arches (Jr 1-5) are very uniform, only decreasing gently in size from 
before backwards. Each is composed of a superpharyngeal, apical piece, the pharyngo- 
branchial, an epibranchial, a ceratobranchial, and a hypobranchial on each side (p.br, 
e.br, c.br, h.br). These arches are strongly bowed outwards, and bent on themselves; 
their lateral parts are thick, and grooved externally. A single series of cartilaginous 
