RANA. 347 
The ‘second and third unite to form a brachial plexus to 
the fore-limb ; the fourth, fifth and sixth pass to the body- 
muscles ; the seventh, eighth and ninth unite to form the 
sciatic plexus continued into the hind-limb. The tenth is a 
small spinal beside the wrosty/e. On either side of the aorta 
is a thin pigmented nerve-chain with ganglia, called the syz- 
pathetic system. From each ganglion a connection passes 
to each spinal nerve. Forward, the sympathetic chain ter- 
minates in the Gasserian ganglion of the fifth cranial nerve. 
The ten cranial nerves are essentially like those of the 
skate, though smaller and more difficult to follow, and the 
fifth, seventh and tenth nerves are much simpler. The fifth 
has three main branches—the ophthalmicus, the maxillary 
and mandibular. The sevénth has only two main branches 
—the palatine and the hyomandibular. The vagus has no 
branchial branches, but supplies the larynx, lungs, heart 
and stomach. 
At the sides of the vertebree are a number of masses of calcareous 
matter called cakareous bodies. They have a curious developmental 
connection with the ear. 
‘The brain may be seen by removing the dorsal bones of 
the cranium. It is small and has a very small cerebellum. 
The various parts are in one horizontal axis and do not 
overlap each other. 
The spinal cord passes down the vertebral column, as in 
the skate, and terminates in the uvostyle. 
The frog has no exoskeleton. The endoskeleton can, 
as in the skate, be divided into axial and peripheral parts. 
Skel The axial is composed of a skull and vertebral 
etal. : 3 
column. The skull is composed of the cranium 
and the first two visceral arches, mostly joined together. 
The first important difference from the skull of the skate 
is the presence of bones in addition to the cartilaginous por- 
tion. Some of these bones are formed in dermal membrane 
and sink on to the cranium; these are called membrane- 
bones. The others are formed in the cartilage, or rather 
they replace the cartilage which is destroyed as they grow. 
These are termed carttlage-bones. The cartilage may be seen 
extending between the bones, or the membrane-bones may 
be removed, in which case the true extent of the cartilaginous 
cranium can be clearly seen. The actual cranium is small 
