146 On the Evolution of the Vertebrata, [February, 
reptiles in the larger cerebellum, with rudimental lateral lobes. 
The great development of the hemispheres in birds is well known, 
while the general superiority of the brain of the living Mamma- - 
lia over all other vertebrates is admitted, 
The consideration of the successive relations of the skeleton in 
the classes of vertebrates embraces, of course, only the charac- 
ters which distinguish those classes, These are not numerous. 
They embrace the structure of the axis of the skull; of the ear 
bones; of the suspensors of the lower jaw; of the scapular arch and 
anterior limb, and of the pelvic arch and posterior limb. Other 
characters are numerous, but do not enter into consideration at 
this time. 
The persistence of the primitive cartilage in any part of the 
skeleton is, embryologically speaking, a mark of inferiority. From 
a physiological or functional standpoint it has the same signifi- 
cance, since it is far less effective both for support and for move- 
ment than is the segmented osseous skeleton. ' That this is a> 
prevalent condition of the lower Vertebrata is well known. The 
bony fishes and Batrachia have but little of the primitive cartilage 
remaining, and the quantity is still more reduced in the higher 
classes. Systematically then, the vertebrate series is in this 
respect an ascending one. The Leptocardii are membranous; 
the Marsipobranchii and most of the Elasmobranchii cartilagin- 
-ous; the other Pisces and the Batrachia have the basicranial axis 
cartilaginous, so that it is not until the Reptilia are reached that 
we have osseous sphenoid and presphenoid bones, such as char- 
acterize the birds and mammals. The vertebral column follows 
more or less inexactly the history of the base of the skull, but its 
characters do not define the classes. = 
As regards the suspensor of the lower jaw the scale is in the 
main ascending. We witness a gradual change in the segmenta- 
tion of the mandibular visceral arch of the skull, which clearly 
has for its object such a concentration of the parts as will produce 
the greatest effectiveness of the biting function. This is accom 
plished by reducing the number of the segments, so as to bring 
the resistence of the teeth nearer and nearer to the power, that is, 
the masseter and related muscles, and their base of attachment, the 
brain-case. This is seen in bony Vertebrates in the reduction of 
~ the segments between the lower jaw proper and the skull, from 
four to none. In the fishes we have the hyomandibular, the sym- 
