794 SEC. 18. BIOLOGY. 



twelve times iu different positions, all the air can be pumped out and the 

 cavities completely filled with fusible metal. The bone is now removed from 

 the bath of fusible metal, and the adherent metal removed. It is then placed 

 in melted paraffin, so as to cover the steel plates, and the greater part of the 

 mastoid portion. When the paraffin has solidified, the whole is placed in a 

 vessel containing dilute hydrochloric acid. This dissolves the unprotected 

 part of the bone, leaving a cast of the cavities in fusible metal. From thie 

 the casts of the mastoid cells are,carefully removed. To the external part of the 

 mastoid is now soldered a brass pin fitting into a socket in , the large gonio- 

 meter. The cast can then be brought successively into positions in which 

 each of the canals lies in a horizontal plane. In each of these positions the 

 skull is replaced by means of the steel plates, and a glass plate fixed to the 

 skull in a horizontal plane. These plates are therefore parallel respectively 

 to the planes of the canals ; and their relative position can be ascertained by 

 means of the goniometer. See Proceedings of the Royal Society of Edinburgh, 

 January 1874, and Journal of Anatomy and Physiology, viii. 327. 



3734. Skull of Owl, prepared to show relative position of the 

 semicircular canals of internal ear. 



The strongly osseous tissue has been removed from the dense bones forming 

 the canals, and these have been coloured so as to indicate the pairs of parallel 

 canals. 



3735. Skull of Crow, prepared to show relative position of 

 the semicircular canals of internal ear. 



3736. Skull of Heron, prepared to show relative position of 

 the semicircular canals of internal ear. 



3737. Cast, in plaster of Paris, of internal ears of the skate. 



3738. Apparatus for measuring the relative position of the 

 planes in which the semicircular canals of the internal ear 



are situated, with skull, illustrating its application. 



The apparatus is simply a reflecting goniometer on a large scale. The 

 telescope used with it is not sent, as it requires to be fixed at a considerable 

 distance from the apparatus. 



The mode of preparing the ear for observation is described above. 



3739. Cast, in solder, of human internal ear, right side. 



3740. Dynamometer for Faracentesis Thoracis, by Dr. 



Douglas Powell. T. Hawksley. 



3741. Dr. Douglas Powell's Instrument for measuring 

 Thoracic Resilience. T. Hawksley. 



3 741 a. Instrument for the Identification of Persons. 



Joseph Bonomi, 13, Lincoln's Inn Fields, W.C. 



The normal proportion of the human frame is that the measure of the dis- 

 tance from the extremity of one hand to the extremity of the other when the 

 arms are extended should be the same as that from the top of the head to the 

 sole of the foot, and any departure from this normal proportion furnishes 

 a means of individual identification. 



