NOTE ON THE DEVELOPMENT OP AMPHIBIANS. 319 
more than half as far as the first branchial bar, so that in the 
sections of series h it first appears in the section 30 h. Each 
of these five bars is supported dorsally by a small muscle ; the 
muscles are shown at in' . in! . in fig. 27 h. Dorsally the four 
branchial bars are united by a continuous piece of cartilage, 
c. b., fig. 27 h. None of these bars are articulated into different 
pieces, but the hyoid and first two branchial bars show ventrally 
a rudimentary beginning of an articulation. 
The cranial skeleton of Amblystoma at this stage shows 
certain peculiarities, the homologies of which I am unable to 
determine in other forms. A general idea of the shape of the 
skeleton may be derived from fig. 31 and series H. Each 
lateral half of the cranial skeleton, together with the corre- 
sponding quadrate, appears as one continuous piece of carti- 
lage. Of this piece the parts corresponding to the trabecular 
( tbr .) and parachordal ( prc .) cartilages are easily distinguished; 
the former lying along the anterior surface of the brain, and 
the latter lying along the floor of the hind- brain adjacent to 
the notochord. The trabeculae do not meet anteriorly. From 
the anterior end of the parachordal region there extends in a 
dorso-lateral direction a small bar of cartilage (x, figs. 31 and 
28 h). This is met by another bar of cartilage (y), which 
extends upward and backward from the trabecula at the region 
of the optic nerve. These two bars (x and y) form thus a 
triangle, of which the base is the posterior part of the trabe- 
cula. At the junction of the anterior bar ( y ) with the trabe- 
cula there is a foramen through which passes the optic nerve 
(n. II, fig. 31). The greater part of the bar marked y. 
appears to pass dorsal to the optic nerve (fig. 31). This bar is 
a relatively thin piece, and separates the eyeball from the 
thalamencephalon. The posterior bar ( x ) of the triangle lies 
in the lateral groove between the floor of the hind-brain and 
the infundibulum, that is, lateral to the fold caused by the 
primary cranial flexure. At the dorsal apex of this cartila- 
ginous triangle the cartilage is continuous with the dorsal 
proximal part of the quadrate cartilages (Q.). This is seen at 
Q. x, y, in figs. 27 h and 28 h. The dorsal part of the quad- 
