VOL. XXXr.] PHILOSOPHICAL TRANSACTIONS. 445 



ordinary refraction of the star is l' 55^^, or 115''; and the barometer rising and 

 falling above 2 inches in 30, shows that the density of the air, on that score, 

 may be a 15th part more at one time than another. Whence the refractions 

 being always proportional to the density of the medium, as we have all seen it 

 often demonstrated by Mr. Hauksbee, both in vacuo, and in a doubly and 

 trebly condensed air, it is plain that in that altitude the refraction of a star may 

 differ about 7 or 8 seconds, or the 15th part of 1 15", which is more than the 

 whole parallax supposed to have been observed. 



It were to be wished that Mr. Cassini would please to try this matter by the 

 Lucida Lyrae, instead of Sirius, which, though somewhat less than him, is as 

 near to the Solstitial Colure, and has much greater latitude, being only 28*^ from 

 the pole of the ecliptic, whence its parallax would be so much greater ; and 

 being at Paris within 10° of the zenith, the grand objection of the difference 

 of refraction would be almost wholly removed. 



jin Account of the external Maxillary, and other Salivary Glands: also of the 

 Insertions of all the Lymphatics, both above and below the Subclavians, into 

 the Feins. By Richard Hale, M.D. F. R.S. N« 364, p. 5. 



The external maxillary glands in brutes are of the conglomerate kind. They 

 lie externally, laterally (lengthwise) on the lower jaw, partly under the depressor 

 labiorum, and partly under the buccinator. A strong membrane intervenes 

 between these glands and the jaw on one side, and between them and the buccal 

 glands on the other side. They are more or less red, like the pancreas, ac- 

 cording to the quantity of blood that remains in them ; otherwise their sub- 

 stance is white. 



These glands receive arteries from the external carotids, veins from the 

 external jugulars, and nerves from the third branch of the par quintum. 



The number of excretory ducts from these glands is not always the same in 

 the same species of animals. In cows generally 14 are discovered by the probe. 

 Their orifices are valvular, about 4 times less than their ducts; Every duct is 

 about half an inch from the next. Those in the middle of the glands are largest, 

 because the glands are there broadest and thickest. The ducts do not com- 

 municate with each other, nor with the buccal. Every duct is formed of lesser 

 ducts united, which rise from the lobules, through the whole substance of the 

 glands, which constitute each distinct lobe, and has the same structure as the 

 pancreatic duct. Each lobe is depressed on its sides, where it is joined to other 

 lobes ; and between the lobes many buccal glands are interspersed. 



In calves, seldom more than 6 or 7 ducts admit any probe ; when the animal 

 grows older, the ducts appear more plain and open. 



