LECT. VIII.] AN UNFOLDED BAT. 191 



are worthy of a whole course of lectures ; I can only 

 refer to one or two points in their structure. In the 

 embryo of a small kind of Bat, from North America, 

 no larger than the grub of a Blue-Fly, the curious, 

 expanding, hands are rapidly developing, and the folds 

 of the skin are all growing, so that the embryo is quite 

 comparable to the unfolded bud of a plant. Like the 

 Mole at the same stage, this type shows its hereditary 

 characters very early. There is one point in the 

 anatomy of the Bat which puts it on a similar level to 

 that on which we find the Shrew, namely, that there is 

 a considerable rudiment of the coracoid bone attached 

 to the large, keeled "manubrium" (top part) of the 

 breast-bone. This is, as we saw before, the remnant of 

 a structure largely developed in the Monotremes (Duck- 

 bill and Echidna). 



The skull of the Bats is intensely ossified and anchy- 

 losed, as in the Flying Cat, and as in Birds. There is 

 a chain of small tympanic bones, as in the Crow tribe ; 

 besides a cartilaginous bulla tympani (or second inner 

 chamber of the ear-drum), and a bony annulus 

 tympanicus ; neither of the two last parts exist in the 

 Bird. But the special adaptations seen in this kind of 

 Mammal for the purposes of flight, are out of the 

 way of any properly ascending survey ; they are a 

 sort of side-branch of the life-tree of the Mammalia. 



