6' Mr. Home's Lecture 



the vessels had been most successfully injected with coloured 

 wax. 



In this preparation, the most beautiful of the kind I ever saw, 

 ► the vessels in their distribution resembled those of the iris, and 

 were nearly half as numerous : they anastomosed with one an- 

 other in a similar manner, and their general direction was from 

 the circumference to the handle of the malleus ; from near this 

 handle, a small trunk sent off branches, in a radiated manner, 

 which anastomosed with those which had an opposite course. 



This correspondence, in the number and distribution of blood- 

 vessels, between the membrana tympani and the iris, is a strong 

 circumstance in confirmation of that membrane being endowed 

 with muscular action. 



In the horse, the membrana tympani is smaller than in man ; 



its long diameter is 2 8 o tns °f an ^ ncn > tne snort one 2" 6 o tns » anc * 

 it is almost quite flat, while in man it is concave, which makes 

 the difference of extent considerably exceed the difference in the 

 diameters. In the horse, the fibrous structure is not visible to 

 the naked eye ; it is even indistinctly seen when viewed through 

 a common magnifying glass ; but in a microscope it is very 

 visible, and in every other respect agrees in structure with the 

 membrane in the human ear, and in that of the elephant. 



In birds, the membrana tympani is larger in proportion than 

 in the quadruped, and more circular in its shape. 



In the goose, it is /oths of an inch in its longest diameter, and 

 /oths in its shortest diameter. In the turkey, ^ths by /oths. 

 It is thinner in its coats in birds than in the horse, and to the 

 naked eye has no appearance of fibres ; but, when viewed in a 

 microscope, there is a visible radiated structure, not very unlike 

 the wire marks upon common writing paper. 



