DEVELOPMENT OE THE SKULL IN THE BATKACHIA. 
609 
downwards and forwards into the scooped anterior face of the auditory mass (fig. 3). 
In front the tegmen is continuous with the “ otic process ” of the mandibular pier 
p-)- 
The foramen magnum is largely open on the upperside (fig. 3 thus, being 
oblique, it seems to be a heart-shaped space, for its outline is narrow and rounded above, 
bulging at the sides, and emarginate below. This emargination, where the notochord 
has been aborted, is the end of the parachordal plate, at its middle. On each side of 
this there are the right and left occipital condyles ( oc.c .), having a core of bone and 
a bark of cartilage. 
The exoccipitals are pinched in outside the condyles, and they elegantly expand to 
receive and to enclose the large posterior canals. This is above (fig. 3, e.o., p.s.c .) ; but 
below (fig. 4), the bone, true to its Batrachian nature, occupies all its own and also the 
“opisthotic” territory (see also fig. 7). 
The hypoglossal nerves do not pierce, but pass out behind the occipital ; but the exoc- 
cipital bone enrings the nerves that pass out of the chink between the occipital arch 
and the ear-sac. These are the glossopharyngeal and vagus (9, 10); they are separated 
by a bar of bone, which divides this foramen into two*'. 
The opisthotic region of the exoccipital (figs. 4 & 7, e.o.) is seen below the vestibule, 
in front of the double foramen (9, 10), and outwards to the hinder edge of the stapes 
(fig. 7, st.). Here it is seen growing downwards as a hook, whose concave face is for- 
wards. This roughly represents the bar which, in the higher types, separates the 
fenestra ovalis from the fenestra rotunda, and which, in the Crocodile, forms a ring 
round the neck of the cochlea (Huxley, Elem. Comp. Anat. p. 223, fig. 89, A, Op.O,c , 
Chi.). In fig. 7, where most of the tegmen tympani (t.ty.) has been cut away, the extent 
and relations of those two great bones, the prootic and the exoccipital, are well seen, as 
also how near they come to each other. 
As my views upon the meaning and nature of the parts of the facial bars attached to 
this auditory mass have undergone much change, owing to Professor Huxley’s criticism, 
his own work, and my renewed research, the description that follows will be found to 
differ in several particulars from that given in my paper on the Frog (see also, Huxley, 
“On Menobranchus ,” Proc. Zool. Soc. March 17, 1874, and his article on the “Amphibia,” 
Encyc. Brit, new edit.). 
The dorsal ends of the mandibular and hyoid arches have been the most difficult 
parts to work out, owing partly to developmental anachronism, and partly to their 
relation to the auditory mass, and the metamorphosis dependent upon, and ruled by, 
that relation. 
The manner in which the mandibular pier is attached to the auditory mass is best 
seen from below (fig. 4) ; its apex originally passed into the trabecula, on its outside 
* I must now change the number of the nerves, and pass from the “ old style ” to the new. Henceforth the 
portio mollis is to he marked as 8, and not 7 a, and the glossopharyngeal and vagus 9 and 10, and not 8 a 
and 8 b. 
4 Q 
MDCCCLXXVI. 
