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THE AMERICAN NATURALIST [Vol. XL 



regions, an anterior naso-ethmoidal and a posterior petroso- 

 occipital, regions which are connected by two narrow longitudinal 

 bands in the position of the ethmoids. The space between these 

 bands is the pituitary space, and the bands themselves are ossi- 

 fied in their middle regions to form what we have already described 

 as the ethmoid bones, while their ends are cartilaginous to connect 

 anteriorly and posteriorly with the naso-ethmoid and petroso- 

 occipital regions respectively. 



The naso-ethmoid cartilage serves chiefly as a lining to the nasal 

 chamber, and may be seen in a dorsal view of the skull, over a part 

 of the anterior nares and at the antero-lateral angle of the orbital 



The petroso-occipital region is more extensive, and the cartilage 

 is there thicker than in the naso-ethmoidal region. It forms, as 

 the name would suggest, the cartilaginous basis of the occipital 

 region, and though in the adult it is largely ossified, there is a con- 

 siderable cartilage that persists even in the adult skull. The 

 thickest cartilage is found in the region of the ear, where it forms 

 a large part of the auditory capsule. Various parts of the petroso- 

 occipital region are more or less fully ossified to form the following 

 bones, whose form and position have already been described, and 

 which are described by Osawa in connection with the cartilaginous 

 cranium: the exoccipital (occipitale laterale), the prootic, the 

 quadrate, and the columella. The ethmoid, which forms the 

 middle of the longitudinal bands connecting the petroso-occipital 

 and naso-ethmoidal regions, has also been described in connection 

 with the bony cranium. 



It remains now to describe the bones and the cartilages of the 

 visceral skeleton. 



The Visceral Skeleton 



The visceral skeleton is made up of six arches: the mandibular 

 arch or lower jaw, the hyoid arch, and four visceral arches. It 

 differs, then, markedly from the Japanese species which, accord- 

 ing to Osawa, has only four arches, the last two visceral arches 

 being absent. The visceral skeleton as a whole is large and strong 

 and, though consisting largely of cartilage, it persists throughout 



