FROG : EXTERNAL FEATURES AND BODY- WALL 33 



/"'O. 



bears two membrane bones, one on its upper side and 

 one beneath. The upper bone is known as the nasal, and 

 is shaped like the outline of a pear, with the stalk directed' 

 outwards. The lower bone is the vomer. It is of irregular 

 shape and carries a patch of teeth which project through 

 the skin of the roof of the mouth. 



The auditory capsules are blocks of cartilage continuous 

 with that of the cranium. Each contains a complicated 

 space, the cartilaginous labyrinth, which lodges a structure 

 known as "the membranous labyrinth of the ear." Part 

 of the front of the capsule is ossified to form the prootic 

 bone. Above these there abuts on its outer side a T-shaped 

 membrane bone 



known as the ■?■■'"• 



squamosal, which 

 touches it by one 

 limb of the cross- 

 piece of the T, 

 the main limb 

 being directed 

 outwards and 

 downwards. At 

 one spot on the 

 outer side of the 

 capsule the carti- 

 lage fails and the 

 labyrinth is 

 covered only by membrane. This gap is known as the 

 fenestra ovalis, and from it a slender rod of bone and 

 cartilage, the columella auris, runs to the drum of the ear, 

 so that when the latter is thrown into vibrations by sound 

 waves its movements are transferred by the columella to the 

 labyrinth through the membrane. 



The framework of the upper jaw is composed of two 

 series of structures, an outer, which borders the opening 

 of the mouth, and an inner, which supports the outer. 

 The inner series is known as the palato-pterygo-quadrate 

 on account of the parts of which it is composed. These 

 are as follows. From the junction of the cranium with 

 the nasal capsules there projects outwards a bar of carti- 

 lage, against the hinder, or orbital, side of which lies a 



FIG. 14. — The skull of a frog, seen from 

 behind. 



col., Columella; ex., exoccipital ; f.m., foramen 

 magnum; o.c, occipital condyle; pro., prootic; 

 pt., pterygoid ; q. , quadrate; q.j., 

 sq., squamosal ; IX.X.. 

 tenth cranial nerves. 



j quadrzCtojugal ; 

 foramen For ninth and 



