URINOGENITAL ORGANS 



537 



arising from the wall of the tympanic cavity and inserted on 

 to the manubrium of the malleus. 



The study of development indicates that the malleus corresponds to 

 the articular part of MeckePs cartilage of lower Vertebrates, and the 

 incus to the quadrate (pp. 44 and 438) : the articulation of the bony 



Ex 



FIG. 143. Diagram of the mammalian bony labyrinth, tympanic cavity, and external 



auditory passage. 



Cch. bony cochlea ; E. Eustachian tube ; Ex. external auditory passage ; L. bony 

 semicircular canals ; M. tympanic membrane ; N. auditory nerve ; O\. stapes ; 

 ?2' incus ; O%. malleus. (After Headley.) 



mandible with the squamosal in Mammals has rendered these parts 

 unnecessary for their original purpose, and they have undergone a change 

 of function, forming an accessory part of the auditory apparatus. ' 



Urinogenital Organs. The kidneys (Fig. 135, k] are of a 

 somewhat compressed, oval shape, with a notch or hilus on 

 the inner side. They are in close contact with the dorsal 

 wall of the abdominal cavity, the right being somewhat in 

 advance of the left. Towards the hilus, the tubules of 



