DEVELOPMENT OF THE SKULL IN THE CROCODILIA. 285 
by the hind border; the articular part becomes an oblong sinuous condyle passing 
across, and a little forward, externally (Pl. LXV. figs. 5 & 8, 9g). 
The quadrate bone (q) possesses the body of the cartilage, but not its outgrowths or 
processes ; it is not pneumatic at present. The free articulo-Meckelian rod or mandible 
(Pl. LXV. fig. 8, ar, mk) is nearly as long as the skull, has a saddle-shaped condyloid 
facet (ar.c), a rounded angular process, a bony centre, the “articulare,” and a long, terete, 
Meckelian rod, which is confluent with its fellow in front (Pl. LXVI. fig. 5, mh, b.mn). 
In the coronoid region there is a small, notched, squarish plate of cartilage, the 
“coronoid cartilage” (¢7.c); the rudiment of the continuous coronoid crest of the 
mandible in Lepidosteus and Amia. Meckel’s cartilage is thickest in the middle, and 
is attenuated at each end. 
Another remarkable rudimeut (or remnant) is seen in the upper part of the first 
arch; this is an eatrapterygoid facet (Pl. LXV. fig. 8, and Pl. LXVI. figs. 1 & 3, py.c’); 
this is a tongue-shaped tract lying along the outer edge of the pterygoid bone, where 
it glides against the mandible; it is a partial reappearance of the large ichthyic 
pterygoid outgrowth. 
I shall describe the hyoid arch in both the Alligator and Crocodile in this stage, 
which gives a stapedio-hyoid bar, almost precisely the counterpart of that of Hatteria 
(Pl. LXVIII. figs. 15, 16, Pl. LXIX. figs. 1-3; see also Huxley, Proc. Zool. Soc. 
1869, p. 597, fig. 4). 
In the Alligator (Pl. LX VIII. figs. 15, 16) the stapedial disk of the columella is very 
large and oval; it has its own basistapedial centre (st) on the inside of the disk. The 
mediostapedial bone (m.st) is dilated on the outside of the disk, and forms a shortish 
and slightly curved shaft, which reaches nearly to the distal dilatation of the columella ; 
the segmental line seen at this part, in the earlier embryos, is gone. ‘The bar itself is 
continued upwards and forwards, but grows into a large fan-shaped crest, with a ribbed 
free outer edge; this is the extrastapedial process (¢.st). From its thick (axial) back, 
near its base, the suprastapedial process (s.st') is given off; it is like a half-open fan, 
and grows upwards, inwards, and backwards (see Pl. LXV. fig. 8). Coalesced with 
this, but with the line of junction still evident, we see the suprastapedial cartilage (s.s¢), 
an ear-shaped flap, twice as large as its stalk, and having its narrow lower end free. A 
notch on the outer side of the broad, lower end of the extrastapedial receives the short, 
curved epihyal (¢.hy), and this is joined to a notch on the hinder side of the broad 
upper end of the ceratohyal (c.hy), now membranous in its lower half, and therefore 
quite free from the mandible below. These parts are all continuous (see also in the 
irregular hyoid of another specimen, Pl. LX VIII. fig. 16), and only show the old seams 
of segmentation. 
The most perfectly Hatterian condition is seen in the hyoid arch of an embryo 
Crocodile taken on July 27th (Pl. LXIX. fig. 1). In this elegant stapedio-hyoid - 
structure the stapedial base (st) has its own inner, osseous centre, and a stout bony 
