158 



animal, and hence called cervical ribs. These ribs are about twenty- 

 five in number, and gradually lengthen from the upper end to the 

 tenth or eleventh pair, and then successively shorten to the last. 

 They extend in lateral directions, having only a slight curvature ; 

 and when depressed, lie upon the side of the spine, one on the other. 

 They are raised by four sets of muscles ; and another large set of 

 very long muscles has the power of bringing the skin forward, thus 

 forming the appearance which has been called a hood. Besides these 

 muscles, there are three other sets, by which the hood is depressed, 

 and the parts are restored to that state in which the neck of the 

 animal does not appear disproportionally protuberant. These de- 

 scriptions are illustrated by accurate drawings ; but no conjecture is 

 here given as to the probable uses of this singular mechanism, except 

 that it does not appear to promote in any way the play of the lungs, 

 but that the expansion it produces may perhaps facilitate a dilatation 

 of the gullet, for the purpose of allowing the snake to swallow its 

 prey more easily. 



Continuation of an Account of the Changes that have happened in the 

 relative Situation of double Stars. By William Herschel, LL.D. 

 F.R.S. Read June 7, 1804. [Phil. Trans. 1804, p. 353.] 



In the former part of this paper, Dr. Herschel mentioned the 

 changes he had noticed in the situation of six double stars ; and in 

 investigating the causes of those changes, he declared that he had re- 

 course to the most authentic observations he could find of their motions 

 in right ascensions and polar distance, especially in the instance of the 

 double star Castor : but finding in the tables which have been lately 

 published in the last volume of the Greenwich Observations, which 

 give the proper motions of thirty-six stars, that (especially in the in- 

 stance of the above-named star,) the motions are somewhat different 

 from those he assigned to them in his former communication, he now 

 undertakes to review the arguments he there used, in order to ascer- 

 tain what will be the result of these new motions. As this investi- 

 gation, which forms the first part of the present paper, has a con- 

 tinual reference to the contents of the preceding one, it will be in 

 vain to attempt an abridgement, which could not be rendered intel- 

 ligible within our usual limits. Nor can we enter here into a detail 

 of the sequel of Dr. Herschel's observations on the changes in the 

 situation of a great number of additional double stars ; this second 

 part of the paper, in which they are fully detailed, being itself a 

 minute of his proceedings, in which he is at particular pains to point 

 out that these changes of situation are not the effect of parallax. 



