57^ PHILOSOPHICAL TRANSACTIONS. [aNNO 17 10. 



the performance of the rational and animal functions; and in the other, had 

 the quantity of brains been greater, the principia nervorum had been more 

 divided; so that instead of being requisite, they had been vastly inconvenient, 

 because the nerves could not so well receive the spirits dispersed in a greater 

 mass, as now, when contracted within less bounds. 



The inner surface of the skull, where the brain is lodged, is in figure like a 

 human skull, but more spherical, being from the right to the left 10 inches, 

 from front to back Q inches, and from above to below at the anterior fossa 7 

 inches, between the middle 5 inches, and at the posterior, or seat of the cere- 

 bellum, 4-i- inches. It has 4 fossae, and 5 eminences. The anterior fossa is 

 circumscribed by the fore part of the inner table of the skull before, and by the 

 two anterior eminences behind. Here the brain sends forth its greatest pro- 

 duction; for at the hind part this anterior fossa is depressed straight down near 2 

 inches, where the os ethmoides begins, which is of a singular figure and struc- 

 ture ; for from the fore part of the seat of the brain in the middle, there 

 is here, as in most skulls, an eminence which runs obliquely downward, till it 

 begins to form the crista galli, so called in human subjects. This crista galli 

 divides the os ethmoides into its right and left part ; it is pretty thick and broad 

 at the base, whence it rises from each side, till it begins to form a crena, which 

 is perforated by 3 pair of holes ; and then there arises a small spina in the mid- 

 dle, at the fore extremity whereof, it being further extended than the ethmoides, 

 there is another hole. From this crista galli run on each side several prominent 

 convex lines, some obliquely forward, others obliquely backward, others trans- 

 versely ; each of which is branched out twice or thrice toward the circumfer- 

 ence. These lines have some few perforations running from their highest part, 

 but most of them are between their interstices, where they are pleasantly 

 dispersed after some kind of order, which we could not express in the figure. 

 The OS ethmoides is not unlike a heart, as they usually represent it, being 

 narrower at the hind part, where the anterior fossa runs straight down from the 

 fore part of the sella turcica, and broader at the fore part of the bone, which 

 runs obliquely upward from it; it is from front to back 3-^ inches, and from the 

 right to the left 4 inches : its circumference is not altogether circular. 



The parts of the ear, are, 1st. The meatus auditorius, or that duct which 

 runs from an orifice on each side of the head, to the inner table of the skull, 

 terminating in the os petrosum, being of a cylindrical figure, having the cellules 

 arising from it on all sides. It is in length, from the external orifice to the 

 crena for the membrana tympani, 94- inches, and about 1 inch diameter through- 

 out the whole extent. Its sides are composed of a firm solid bone, and little 

 thicker than a halfpenny. Next is observable the crena for the membrana 



