. A manual of elementary zoology . Zoology. FROG : EXTERNAL FEATURES AND BODY-WALL 33 /"' 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 &
. A manual of elementary zoology . Zoology. FROG : EXTERNAL FEATURES AND BODY-WALL 33 /"' 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 ; 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 â ?â â '"⢠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.âThe skull of a frog, seen from behind. col., Columella; ex., exoccipital; , foramen magnum; , occipital condyle; pro., prootic; pt., pterygoid ; q., quadrate; , sq., squamosal ;
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Keywords: ., bookcentury1900, bookdecade1920, booksubjectzoology, bookyear1920
