VOL. XXX.] PHILOSOPHICAL TRANSACTIONS. 385 



seat of the brain (b). This is 20 lines or 1 inch 8 lines long. The medius 

 ductus, one part whereof regards the orifice of the cochlea, and the other is 

 common with the major for the space of 3 lines; (e) this is 15 lines or ] inch 

 3 lines long; and the minor, which regards the cavitas tympani, has one orifice 

 which is near to the medius, where it approaches the cochlea, and the other 

 near to the orifice of the major; this is 1 inch long. 



The seventh pair of nerves, called in general the nervus auditorius, enters 

 the processus petrosus, and is divided into the hard and soft portions, as in 

 other animals. In this subject I find one canule entering the bone from the 

 sides of the orifice for the carotid artery, about 3 lines diameter (e) (h), from 

 thence running forward for the space of I inch 4 lines, then bending down- 

 wards 1 inch, till it meets with the orifice at the sides of the meatus auditorius, 

 by which it pierces the skull, and passes outward. This canule, after it has 

 entered the processus petrosus for the space of 8 lines, communicates with the 

 orifice, which usually enters the aforesaid process from the base of the skull; 

 and both these orifices, after they have accompanied one another about 5 lines, 

 are separated, and the soft portion penetrates the bone at two places, as is said. 



Explication of the Figures. 



Fig. 8, pi. 9j represents the bony part of the meatus auditorius of the right ear; a the external 

 orifice of the meatus auditorius j b the processus petrosus j c the orifice where the nervus auditorius 

 enters i d the meatus auditorius } e a part of the laminae which proceed from it on each side, by 

 which the cellules between the two tables of the skull are formed, tliose situated above the meatus 

 being removed j f part of the inner table of the skull. 



Fig. 9> represents part of the meatus auditorius opened, with other parts of the inner earj a the 

 ragged part of the bone, from whence the os petrosum was separated j b the processus petrosus 

 opened} c the crena for the membrana tympani j d the honeycomb cavity of the tympanum j e its 

 inner cavity of a smooth surface; f its semicircular or undulated lines; g the orifice of the aqueduct; 

 h the orifice of the hard portion of the nerve. 



Fig. 10, represents the lower surface of the os petrosum, as it was separated from above the tym- 

 panum and other parts of the inner ear; aa the ragged margin of the bone; bb the upper part of the 

 cavitas tympani; c the foramen ovale; d the protuberance in which the labyrinth and cochlea are 

 lodged; e the orifice of the hard portion of the nervus auditorius. 



Fig. 1 1, represents the malleolus alone in its true dimensions ; 1 the protuberant head; 2 the semi- 

 circular sinus between it and the margin; 3 the sinus which receives the head of the incus; 4 the 

 angle below the sinus for the head of the incus; 5 the angle where the manubrium malleoli begins; 

 6 the manubrium malleoli. 



Fig. 12, represents the incus; 1 the head of the incus; 2 the sinus or neck of the incus; 3 two 

 apophyses; 4 a long protuberance with the sinus for the os quadrangulare at its extremity. 



Fig. 13, represents the stapes; 1 the small part of the stapes, where it is articulated with the 

 incus, with a sinus at its extremity, being the other half of the cavity for the os quadrangulare; 

 2 2 two small portions of the stapes, where it is articulated with the basis ; 3 tlie basis of the stapes 

 separated; 4 the whole stapes. 



Fig. 14, the malleolus and incus joined together, with their lower side turned up; 1 the malleolus; 



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