CRITICISM OF VERTEBRAL THEORY 161 



the pituitary body is developed ; l in all, the cartilaginous 

 cranium has primarily the same structure a basal plate 

 enveloping the end of the notochord and sending forth 

 three processes, of which one is short and median, while the 

 other two, the lateral trabeculae, pass on each side of the 

 space on which the pituitary body rests, and unite in front 

 of it ; in all, the mandibular arch is primarily attached behind 

 the level of the pituitary space, and the auditory capsules are 

 enveloped by a cartilaginous mass, continuous with the basal 

 plate between them. The amount of further development to 

 which the primary skull may attain varies, and no distinct 

 ossifications at all may take place in it ; but when such 

 ossification does occur, the same bones are developed in 

 similar relations to the primitive cartilaginous skull" 

 (p. 573). 



In a word, there is a general plan or primordial type 

 which is manifested in the higher forms most clearly 

 in their earliest development an embryological archetype 

 therefore. 



Huxley now goes on to consider the relation of this 

 general plan or type of the skull to the structure and 

 development of the vertebral column. Does the skull in 

 its development show any signs of a composition out of several 

 vertebrae? The vertebral column develops as a segmented 

 structure round the notochord ; the skull develops first as an 

 unsegmented plate extending far beyond the notochord. 

 The processes of this basilar plate, the trabeculae, are quite 

 unlike anything in the vertebral column. It is true that 

 when the process of ossification begins, separate bones 

 are differentiated in the basilar plate one in front of the 

 other, giving an appearance of segmentation. The hindmost 

 of these bones, the basioccipital, ossifies round the notochord, 

 quite like a vertebral centrum, and its side parts which 

 form the occipital arch develop in a "remotely similar" 

 way to the neural arches of the vertebrae. The next bone, 

 however, the basisphenoid, develops in front of the notochord, 

 and shows very little analogy with a vertebral body. The 

 analogy is even more far-fetched when applied to the axial 



1 The origin of the pituitary body from the roof of the mouth was first 

 described by Rathke (1839). 



