PHYLOGENY. 95 



while the general superiority of the brain of the living 

 Mammalia 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 characters 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 significance, since it is far 

 less effective both for support and for movement than 

 is the segmented osseous skeleton. That this is a prev- 

 alent 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 ascend- 

 ing one. The Acrania are membranous ; the Marsi- 

 pobranchii and most of the Elasmobranchii cartilagi- 

 nous ; 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 characterize 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 segmentation of the mandibular visceral arch of 



