310 



about two thirds of the length of the lower jaw backwards from the 

 symphysis, being a longitudinal slit a little within the lower edge 

 of the basis of the jaw, and through it exudes an unctuous substance 

 of the consistence of suet and the smell of musk. During warm 

 weather, when the animal feeds freely, the secretion is copious ; but 

 in winter is much diminished in quantity, and less powerful in scent. 



The gland, on removing the integuments, is seen lying between the 

 skin and under-surface of the tongue. It consists of a simple follicle 

 or sac, of a blueish colour, and an elongated and pyriform shape. In 

 an alligator four feet in length, it is about half an inch long and one 

 sixth in diameter. It is lined with a soft secreting membrane. 



The gland is enveloped by extremely fine, delicate, muscular 

 fibres, disposed obliquely, and consisting of two fasciculi, passing re- 

 spectively over and under the gland, and uniting at its base into a 

 long slender round muscle, which, after making a slight curve for- 

 wards, proceeds directly back to the corner of the os hyoides, to 

 which it is closely united; and following the course of another 

 muscle apparently identical with the mylo-hyoicleus in mammifera. 

 The use of the, muscle seems to be to bring the gland into a proper 

 position for discharging its contents, and to operate such discharge 

 by its pressure. 



The author, taking into consideration the situation of the gland 

 near the mouth of the alligator, its predatory habits and voracity of 

 fish, and the well-known partiality of fish for odoriferous oils and 

 extracts, conceives that the use of this secretion is to act as a bait, 

 and attract the fish to such a position that he can easily seize on them, 

 in his usual way of seizing his prey, by snapping sideways at them. 



On the Permeability of Transparent Screens of extreme Tenuity by ra- 

 diant Heat. By William Ritchie, A.M. Rector of Tain Academy. 

 Communicated by J F. W. Herschel, Esq. Sec. R.S. Read March 

 8, 1827. [Phil. Trans. 1827, p. 139.] 



The author states in this paper, that invisible radiant heat, from 

 sources at elevated temperatures, freely permeates thin transparent 

 screens in the same manner as light ; but that as this doctine, esta- 

 blished by Profesor Prevost and M. de la Roche has been contro- 

 verted, he thinks it necessary to demonstrate it by fresh experiments : 

 to this end he covered a small aperture with a film of glass almost 

 iridescent, and keeping it constantly cold, by blowing on it, below 

 the temperature of ambient air, he found that an air-thermometer on 

 one side of it was not affected by a heated iron ball on the other, if 

 the temperature of the ball was low ; but that as this temperature was 

 raised, though not to the point of visible ignition, the effect on the 

 thermometer became sensible and even considerable. 



In another experiment, two air-thermometers, having their bulbs 

 transparent, and as thin as possible, were placed equidistant from a 

 heated ball just ceasing to be visible in the dark. The one was clear, 



