OF THE SKULL IN SHARKS AND SKATES. 217 
A difference is to be noted at once; for the spiracular cartilage is developed in the 
posterior fork of the first visceral arch, and this nucleus in the anterior fork (Pl. XXXV. 
figs. 1 & 4). 
The mandibular nucleus looks outwards and backwards (sp.c); but this is turned 
directly forwards at right angles to the main bar (fig. 4, /.m, hy. Compare also here 
the adult skull, Pl. XLI. fig. 4, mtpg, hm); the “metapterygoid” is the same as the 
spiracular cartilage in the Skate). 
The main hyoid bar is a slender tape of cartilage, pointed finely at each end, and 
far from the mid line at both ends; it is undivided at present. 
The next five arches are the ordinary branchials: the first is much larger than the 
hyoid; and then they gradually lessen, the last being very small. 
These arches are strongly bent upon themselves, the pharynx of the embryo Skate 
being a depressed pouch with extensive lateral fissures or clefts (figs. 1, 2 & 4). 
The main part of each arch is pointed above, the point looking slightly forwards, and 
blunt below, this rounded lobe looking backwards; both ends come much nearer to the 
mid line than in the hyoid arch. In the roof of the pharynx, where the front clefts 
close, there is, just above each main branchial, an independently chondrified piece—the 
Ce pharyngo-branchial ” (p.br); each piece is lunate, pointed outside, blunt within, and 
having its point turned more backwards than outwards, although their general direction 
is transverse. 
These free cartilages cannot very safely be considered as the serial homologues of those 
above the two first arches; they are not at the side of the face, but right beneath the 
edges of the parachordals, where the leashes of nerves are given off (figs. 3 & 4). 
A separate cartilage, developed at the end of the pterygo-quadrate, or one above the 
point of the main hyoid, would correspond more truly. 
The further segmentation and metamorphosis of the skull and its arches will now be 
described. I have shown above what, from the beginning, was independently chondri- 
fied, and now will show how the main bars break up. 
Second Stage: Embryo of Raia maculata, 4 inches long; body 1y in., tail 25 in. ; 
time from deposit of egg-pouch 3 months. 
This important specimen was taken for me from the Brighton tank by the same 
valued friend, Mr. H. Lee; and although the time of its growth was less than twice 
that of the early specimen, the development and metamorphosis was quite perfect— 
that is, as to chondrification and segmentation. 
There is much that is instructive to the morphologist in the external characters of 
this embryo (Pl. XL. figs. 1 & 2, drawn as far as to the umbilicus, w). In front the 
beak has become fixed to the anterior angle of the outspread, gigantic, flabelliform 
pectoral fin (p,f’), which is seen curling round the depressed cheek. Above, the beak 
is seen to be separated by a deep crescentic sulcus from the rounded cranial sac ; and 
