470 CLASS REPTILIA. 



fixed on a particular bone, which does not allow it much 

 power of moving. It is supplied from certain mucous cells, 

 with an abundant viscosity. 



The apparatus of hearing seems to differ but little from that 

 of chondropterygian and bran chiostegous fishes. Under the skin 

 and muscles is found, in the temporal region, a cartilaginous 

 operculum, not rounded, but rhomboidal, and encased in a 

 separate osseous piece. More deeply is a cavity, invested 

 with a greyish pulp, in which is a kind of lodge for a rudi- 

 mentary small bone of the tympanum. This is white, soft 

 and chalky, and effervesces with acids. Still more deeply 

 is situated the first cavity of the vestibulum, which communi- 

 cates with the mastoidian cell, then come the three semicir- 

 cular canals, and, finally, two labyrinthian cavities, one of 

 which is internal and elliptical. 



The heart of this reptile is enclosed in a peculiar pericar- 

 dium. It is more or less globular, and has but a single 

 auricle, and a single ventricle. Its colour is red. A large 

 vena cava, which receives the blood of the pulmonary veins, 

 opens into the auricle, the parietes of which are much less 

 thick than those of the ventricle, which gives rise to the 

 aorta. The lymphatic system is but little known. 



The lungs are convergent in front, and divergent behind. 

 They are composed of small membranaceous cellular sacs, 

 which are often secondarily divided by incomplete partitions, 

 communicating one with another. They receive the air 

 through a short and narrow trachea. 



The liver is situated towards the middle of the body, not 

 far from the point of the heart. It almost covers the lungs. 

 It is convex externally, and concave within, and its figure is 

 that of an irregular trapezoid. It is suspended in the thoraco- 

 abdominal cavity, by a double fold of the peritoneum. 



The bile is green, acrid, and bitter. The kidneys, situated 

 on each side of the vertebral column, are narix)w in front, but 



