Theory of the Vertebrate Skull 129 



the great groups of vertebrate animals, in fishes, am- 

 phibia, reptiles, birds, and mammals, Huxley did im- 

 portant work. Much of this is embodied in his treatise 

 on Vertebrate Anatomy, but to some particular parts of 

 it special attention may now be directed, as much be- 

 cause these serve as excellent examples of his method 

 of work as because of their intrinsic importance. 



The skull is the most striking feature in the skeleton 

 of vertebrate animals, and to the theory and structure 

 of the vertebrate skull Huxley paid special attention, 

 and his views and summary of the views of others form 

 the basis of our modern knowledge. This work was 

 put before the public in the course of a series of lectures 

 on Comparative Anatomy given in 1863, while Huxley 

 was Hunterian Professor at the Royal College of Sur- 

 geons, and the beginnings of it were contained in a 

 Croonian lecture to the Royal vSociety in 1858. 



The theory of the skull which held the field was 

 known as the vertebral theory. The great bulk of the 

 nervous S3^stem of vertebrate animals consists of a mass 

 of tissue lying along the dorsal line of the bod}^ and 

 enclosed in a cartilaginous or bony sheath. The nerve 

 tissue is the brain and spinal cord ; the sheath is the skull 

 in front and the vertebral column along the greater part 

 of the length of the animal. The brain may be taken 

 simply as an anterior portion of the nerve mass, corre- 

 sponding in a general way to an expansion of the spinal 

 cord in the region of the anterior limbs and an expan- 

 sion in the region of the hind limbs, the latter indeed 

 having recently been shown in some extinct creatures 

 to surpass the brain in size. In a similar simple 

 fashion the skull may be taken as an expanded anterior 

 part of the vertebral column, serving as an expanded 

 box for the brain, just as in the regions of the pectoral 



