DEVELOPMENT OE THE SKULL IN THE BATKACHIA. 
619 
on the outer edge of the trabecula with the inner face of the quadrate (g.) near the hinge. 
This ligament is cartilaginous in the next type (Dactylethra), and is an important 
structure in JRana jgipiens and Pseudis paradoxa. Between this ligament and the broad, 
flat, pterygo-palatine band we see the valvular “ inner nostril ” (i.n.). In the former 
stage the trabecular elbow was the greater of the two ; now it is the mandibular, 
which projects most (fig. 4, pd.), the fastened band running in a loop-like manner a 
little distance in front of the ear-sac ( au .), arching round its front convexity. The 
second bar thus, in an outwardly arched manner, curves inwards to the other, or 
pterygo-palatine binder; its last fifth is free; this is the quadrate cartilage ; it ends in a 
rounded condyle, on which the sinuous face of the free mandible (mk.) is hinged. At 
the middle of its side and a little below there is a notch and a subconcave facet, in 
which the hyoid ( c.hy .) rolls ; between them there is a joint cavity. Above this part 
is the “ orbitar process;” this will be described in the next stage (fig. 3, or.p,). The 
small, free mandible ( mk .) is somewhat arcuate, clubbed at its distal end ; has a sinuous 
notch for the quadrate, and a large, solid angular process. 
The hyoid cornu (c.hy.) is an obliquely oblong, massive plate of cartilage, somewhat 
twisted and strongly ridged below for muscular attachment. The antero-superior angle 
has been formed into an oval, gently convex condyle ; the hinder corner is produced 
upwards into a large snag. Below, it is pedate, the sharp and somewhat upturned toe 
looking forwards. The hinder margin of the plate is gently concave, and the fore edge 
is sinuous. 
The form of the still distinct ear-capsule is now that of a badly-shaped egg, with the 
broad end foremost ; above, the cartilage is imperfect ; below, it is becoming mem- 
branous at one point, although well chondrified on the whole. 
This imperfect space is near the front and outer margin, a little behind the elbow of 
the mandibular pedicle ; in it the cartilage-cells are being sundered, and the vacant 
place, the beginning of the “ fenestra ovalis,” is filled in with gelatinous tissue *. From 
this scooped space, backwards, the capsule is bevelled towards the edge ; that projecting 
edge is the “ tegmen tympani.” Both the 5th and 7th nerves make their escape over 
the interspace between the pedicle and the auditory capsule. 
Skull of Bufo vulgaris. — Third Stage. Tadpoles 5-^ lines long. 
With but little increase in the entire length of the larva in this stage, the size and 
development of the head is remarkable. Most of the description of the last is appli- 
cable to this stage ; but I here display the pattern of the Tadpole Toad’s skull, as 
seen from above, with the hyoid cornua, the free mandibles, and the labials not drawn 
(Plate 55. fig. 3). One thing of great importance strikes the eye at once; this is the 
* When the Tadpole is twice the size of this stage, viz. five sixths of an inch, then the gelatinons ping will 
he an oval Opiate of cartilage — the “ stapes.” My early observations on its formation were faulty; Professor 
Huxley pointed that out to me. We agree now as to the manner in which this plate is formed. 
4 R 2 
