VOL. LVI.] PHILOSOPHICAL TRANSACTIONS. 335 



power of long inspiration seems to be as necessary in the land tortoise as in that 

 of the sea ; because, in many countries where they breed, they are known to 

 go into the ground and lie concealed for several months ; and it is well known, 

 that several species of land tortoises go into ponds or canals in gardens, where 

 they are kept, and remain long under water at pleasure. Of this, Mr. Collinson 

 had instances in his gardens at his country seat : and Dr. P. saw two land tor- 

 toises in the bottom of a circular canal, in the gardens of the palais royal in 

 Paris several times, which were not very large ones, and remained under water 

 many hours together. 



The ingenious Academicians however, in order to verify their sentiments, 

 that one principal use of the lungs in a tortoise is to render it capable of re- 

 maining at any depth in the water at will, made the following experiment ; they 

 locked up a living tortoise in a vessel of water entirely full ; on which there was 

 a cover exactly fastened with wax, from which there went a glass pipe : the vessel 

 being full, so as to make the water appear at the bottom of the glass pipe ; they 

 observed that the water sometimes ascended into the pipe, and that it sometimes 

 descended. Now this could be done only by the augmentation and diminution of 

 the bulk of the tortoise ; and it is probable that when the tortoise endeavoured 

 to sink to the bottom, the water fell in the pipe, because the animal lessened its 

 bulk by the contraction of its muscles ; and that the water rose by the slackening 

 of the muscles, which, ceasing to compress the lungs, permitted it to return to 

 its first size, and rendered the whole body of the tortoise lighter. Dr. P. has, in 

 many kinds of fish, dissected their swimming bladders, and found that in great 

 and small these are vested with a strong muscular membrane, which they are ca- 

 pable of contracting and dilating at will, by which they are able to compress or 

 expand the column of air within very considerably ; this bears some analogy to 

 the detrusor muscle of the human urinary bladder, in contracting itself for the 

 expulsion of the urine. 



Plate 9, fig. 1 , represents the situation and inclosure of the aspera arteria of 

 the wild swan, in a lateral view ; a is the aspera arteria ; b the oesophagus ; c 

 vertebrae of the neck ; d the ossa jugalia ; e the keel of the sternum; h the 

 membranes that support the aspera arteria. Fig. 2, a view of the same, with 

 its progress within the thorax on the sternum. Here a is the aspera arteria, pas- 

 sing in the theca, and doubling round to lie upon the sternum, ending in b, the 

 branchia. Fig. 3, The aspera arteria of the Indian cock. This plication is made 

 between the jugal bones, and not in the breast bones, as in the others, and then 

 the end, with the bronchia, enters the thorax, and lies upon the sternum. Fig. 4, 

 A lateral view of the aspera arteria of a crane, as situated in the cavity formed 

 ill the sternum. Fig. 5, shows the flection of the aspera arteria of the Numidian 

 crane ; having the plication made within the keel of the sternum. Fig. 6, the 

 bifid aspera arteria of the land tortoise. The pipe on each side has a small figure 



