calculated to cut deeper than its Centre. 429 



to ihe cranium in every form or posture, and remove any 

 depressed portion of bone with the greatest safely and speed. 

 Mr. Chne and Mr. Whatley have seen the instrument, and 

 expressed their opinion that it would be found a very use- 

 ful instrua)ent in many operations. 



My business as a surgeon, and pressing avocations in the 

 country, prevent me from staying more than a tew days in 

 London. I should therefore esteem it an additional favour 

 if the Societv would soon take it into consideration, that 

 I may personally explain its use. 



The principle oi this machine will be found useful for 

 many mechanical as well as surgical purposes. 

 I am, sir, 



Your humble servant, 



London, March 24, 1812. ThOMAS MaCHELL. 



To C. Taylor, M.D. Sec. 



Reference to the Engraving of Mr. Thomas Machell's 



annular Saiv, which cuts beyond its ovun Centre. Plate X. 



fig. 1,2,3,4,5. 



Fig. 1, is a view of the saw, its frame, and the wheel- 

 work which actuates it ; fig. 2, is an edge view of it ; fig. 3, 

 is a view of part of the interior work, and figs. 4 and 5, a 

 detached view and section of the saw itself. 



In fig. 1, AB represents a solid arm or rod of iron, 

 which supports the whole instrument : this rod is fitted up 

 in such a manner, that it can be moved in any direction 

 either to raise or lower it, to move it from right to left, or 

 to lengthen it out endways, so that the joint B at the end 

 of it can be placed in any possible situation within certain 

 limits: this joint connects another piece D with AB, and 

 at the end of this is a joint E, the motion of which is at 

 right angles to the former joint, and it attaches the saw 

 frame FG to it: this frame, sec also fig. 2, contains a 

 toothed wheel H, which is turned round by the handle f, 

 and by its teeth actuates a smaller wheel concealed witiiin 

 the frame, but its dimensions are shown by the dotted cir- 

 cle described round the screw a, which is its centre pin : 

 this wheel turns another, Z', (see the section, fig, 3,) and 

 this moves a third wheel, c/, which has a circle of six pins, c, 

 projecting from its face, and these turn round the saw K, 

 by entering into notches made in its edge, so that it is ac- 

 tuated by its circumference instead of its axis, as is the case 

 with ordinary c ire?/ Z«r saws ; its construction is explained 

 by figs. 4 and 5, in which K is the ring or annular saw, 



the 



