CHAPTER III. 



PHYLUM VERTEBRATA* (CRANIATA). 



Chordata in which the dorsal nerve cord extends some distance 

 in front of the notochord, and is expanded at its anterior end into 

 a brain. The axial skeleton is divided into an unsegmented 

 cranial portion, which surrounds the brain, and a segmented 

 vertebral portion which forms the axis of the body and protects 

 the spinal cord. 



The various animals included in this phylum were first put 

 together by Aristotle, who called them " animals with blood " ; 

 he also recognized the possession of a bony or cartilaginous 

 skeletal axis as a common characteristic. But it was Lamarck 

 who first adduced the presence of a vertebral column, as a most 

 important character, and introduced before Cuvier the name 

 of Vertebrata into the science. This term, however, is not 

 entirely appropriate, for in some Pisces the sheath of the noto- 

 chord is not segmented, and there are no vertebrae (Marsi- 

 pobranchii, Dipnoi, some Ganoidei). Nevertheless, the term 

 may fairly be retained, for not only has it the sanction of long 

 usage, but the cases in which the vertebral column is not jointed 

 are few in number and unimportant in character. As already 

 pointed out, the segmentation of the vertebral column is corre- 



* Stannius, Handbook der Anatomic ' der Wirbelthiere, 2nd ed., Berlin, 

 1854. Rathke, Beitrdge zur Bildungs und Entwickelungsgeschichte des 

 Menschen und der Thiere, Leipzig, 1833. Owen, The Anatomy of Vertebrates, 

 3 vols., London, 1866-68. Huxley, A Manual of the Anatomy of Verte.brated 

 Animals, London, 1871. Gegenbaur, Vergleichende Anatomic der Wirbelthiere, 

 Leipzig, 1898, 1901. Zittel, Handbuch der Palaeontologie, Munich, vols. 

 iii., iv., 1887-93 ; and Grundziige der Palaeontologie, Munich, 1895. 

 (English translation, Macmillan and Co., 1900). A. S. Woodward, Out- 

 lines of Vertebrate Palaeontology, Cambridge, 1898. Balfour, Comparative 

 Embryology, vol. ii., 1882. C. S. Minot, Human Embryology, New York, 

 1892. 



