3<8 John Grattan : 



a i, and a 2. — Two lines scribed upon the board A. a 1, passing 

 transversely through the eentral point, indicated by 

 X ; and a 2, backwards therefrom, and perpendicular to 

 a 1. They enable the paper Y, when correspondingly 

 marked, to be removed, and accurately replaced, if requisite. 

 To employ this instrument, let the frame E be turned upon its 

 axis, until the axis of G shall be perfectly horizontal, indicated by 

 the mark upon the edge of E ; touching the point of the arrow 

 upon D ; and by the graduated semicircle J, standing perpen- 

 dicularly at the left hand of the operator as he faces the upright 

 D : then let the stage G be turned upon its axis, until it depends 

 vertically from the extremities of E, when its projecting arm, 

 carrying the thumb-screw N, will be underneath — the whalebone 

 lever M lying loosely upon it above. If a skull be now placed 

 upon its base, centrically on the stage G, with its face towards the 

 operator, and the screws HH be introduced into the external 

 auditory foramina, the bony palate will rest upon the hinge-end of 

 M ; whilst, by means of the thumb screw N, the forked extremity 

 of M can be pressed upon the occipital condyles, with any 

 amount of force requisite to keep the skull fixed and steady. The 

 binding-nuts, II are then to be screwed home, after which the 

 stage G may be rotated completely round its axis, carrying with it 

 the skull, which will not require to be shifted upon the stage in 

 any subsequent operation. Let the carriage Q be now moved, 

 until, upon sliding S backwords and forwards, the point of the 

 pencil U exactly traverses the line A 2. Let it be fixed in this 

 position by passing the pin X through a hole in the foot R, into 

 a corresponding hole in the board beneath, and let the point of 

 the tracer W be adjusted precisely upon a level with the axis of E, 

 which will be when the under edge of the slide V touches the 

 point of the arrow upon T. It will now be manifest, that by 

 rotating the stage G, any portion of the median periphery of the 

 skull may be brought into immediate contact with the point of the 

 tracer W, and the distance of any part of it from the axis of the 

 auditory foramina be read off in inches and tenths upon the grad- 

 uated scale in Q : the angular distance of any one point from 



