MORFHULOGICAL METHOD AND EECENT PKOGRESS IN ZOOLOGY. 591 



a iiio.st welcome fact, -i^mcQ^ ArrJneojjIcnj.i'^ in the possession of a plas- 

 tron, carries the a\'ian tj^pe a stage lower than the Dinosaurs. It is 

 pertinent here to remark -that, inasmuch as in those Dinosaurs (e. g., 

 Coi/tj).s(>(/nafh>fx) in which the characters of the hind limbs are most 

 nearly a^■ian, th(^ pelvis, in respect to its pubis, is at the antipodes of 

 that of all known birds, and the fore limb is shortened in excess of 

 that of Archcvoptt'nj.r itself, the long supposed dinosaurian ancestry 

 for birds must l)e held in a])e3"ance. 



Passing through the Rhynchocephalia to the Batrachia we ha^'e to 

 countenance progress most definite in its results. Th(> skull, the limbs 

 and their girdles are chielly concerned, and this in a very remarkable 

 way. 



In the year 1881 there was mad(^ known ])y Professor Froriep, of 

 Tiiljingcn, the discovery that the hypoglossus nerve of the embryo 

 mammal is possessed of dorsal ganglionated roots. Again and again 

 ha^'e 1 heard Huxley insist on the fact that the ventral roots of this 

 nerve are seiial with the spinal set, but uever did he suspect the rest. 

 It is, however, a most intensely interesting fact that, whereas by a 

 Huxleian triumph the vertebral theory of the skull was overthrown, 

 •n these later Huxleian da3^s the proof of the incorporation of a portion 

 of the verte])ral region of the trunk into the mammalian occiput 

 should ha^'e marked the succeeding epoch in advance, The existence 

 of twelve pairs of cranial nerves which all the Amniota possess in- 

 volves them in this change, and the fact that in all Batrachia there 

 are but ten, enal)les us to draw a hard-and-fast line between ]>atrachian 

 and amniote series. 



It may be urged as an objection that since we have long l)een famil- 

 iar with a fusion of vertabne and skull in various piscine forms, the 

 force of this distinction is weakened. But this can not be, since in 

 respect to the investing sheaths and processes of development which 

 lie at the root of the genesis of the vertebral skeleton, the fishes stand 

 distinct from the Batrachia and Anmiota, which are agreed. So forci- 

 ble is this consideration that it behooves us to express it in words, and 

 I have elsewhere proposed to discriminate between the series of terres- 

 trial vertebi'ate as archa^ craniate and syncraniate. 



Similaily, there is no proof that any 1)atrachian, living or (>xtinct 

 (and in this 1 indude the Stegocephala as a whole), poss(^sses a costal 

 sternum. So far as their d(>velopment is known, the cartilages in these 

 animals called "sternal*' are either coracoidal or sui generis. The 

 costal sternum, like the syncraniate skull, is distinctive of the Anmiota 

 alone. Had the Stegocephala possessed it even in cartilage, there is 

 reason to think it might have ))een preserved, as it has been in the 

 collossal Mososaur Tylosanrnx of the American (cretaceous. When to 

 this it is added that wlnu'eas, in the presence of a costal sternum, the 

 mechanism of inflation of the lung involves the body wall, in its absence 



