A 



38 MAMMALIAN DESCENT. [Lect. IL 



'prize of the work of my life — tlie interpretation of the 

 form of Man and of his vertebrated kindred. For, in 

 reading off the characters of the Ovnitliorliyncliiis, and 

 comparing them with those of the Amphibia, below, 

 and of the Eutherian or high mammals, above, we are, 

 so to speak, breaking the seals of a new scroll, on 

 every line of which we can spell out the letters that 

 go to form that great name — Man. 



That which strikes the morphologist as the most 

 remarkable of all specialisations is the manner in which 

 the mobile jaws of the lower type are exchanged for 

 the fixed countenance of Man and the other mammals. 

 In the more generalised fishes there is but little mobility 

 of the lower jaw ; but that part is carried furthest from 

 the face in such forms as the Sturgeon among the 

 ganoids, and in the osseous fishes generally, where the 

 lower jaw is not close to the head, as in a Skate, but 

 swings upon a large compound pier, that intervenes 

 between the jaw and the skull. But in reptiles and 

 birds, the hinder part of the cartilaginous upper jaw — 

 the rest being in a great measure suppressed — forms a 

 hinge-piece or pier to the inverted arch of the lower jaw. 



In birds, generally, the whole upper jaw being mobile 

 — or flexibly attached to the frontal region of the skull — 

 the levator muscle, at the angle of the jaw, at once 

 dejDresses the lower, and lifts the uj^per, jaw, and this is 

 why these creatures are such skilled fly-catchers. Sir 

 Charles Bell, in his charming work on the human hand, 



