EDWARD COPE 87 



Mammals. Taken as a whole, this is an ascending 

 process ; it corresponds to an adaptation from 

 aquatic to aerial life and to the change from a 

 type of cold-blooded animal to a warm-blooded 

 type. 



The brain and the nervous system also show an 

 evident general progression. As to the successive 

 relations of the skeleton in the various groups of 

 Vertebrates, special attention must be given to 

 the ossification of the base of the cranium, to the 

 suspensory apparatus of the mandibles, to the 

 scapulary and pelviaii arcs, and finally to the limbs. 



The persistence of the primitive cartilage in any 

 point of the skeleton is, embryologically, a mark of 

 inferiority. It is the predominant condition among 

 the lowest Vertebrates. In the Leptocardia the 

 cranium is membranous ; in the Marsipobranchia 

 and in many Elasmobranchia (Dog-fish), it is cartila- 

 ginous ; in the other Fishes and in the Batrachians, 

 the axis of the base of the cranium is still cartila- 

 ginous, and we have to get as far as the Reptiles before 

 we see appear the sphenoid and the bony presphenoi'd 

 characteristic of the Birds and Mammals. The spinal 

 column follows more or less exactly the history of 

 the base of the cranium in this progressive de- 

 velopment. 



There is progression likewise in the structure oi 

 the suspensory apparatus of the mandible. Here 

 the gradual reduction from four to zero of the 

 number of bones in the mandibular visceral arc has 

 the effect of shortening the arm of the lever, and 

 increasing its functional power. In the Fishes we 

 note a hyomandibular bone, a symplectic, a lower 



