578 



MR. J. B. SUTTON ON THE DEVELOPMENT [JuilC 2, 



extending from the margin of the foramen magnum to the summit of 

 the dorsum sellse — is composed of the same elements as the vertebral 

 column, but diifers from it in that it has not passed through 

 any stage of vertebiation', the notochordal ])ortion with the jiara- 

 chordals representing the centrum, with the laminse which meet 

 dorsally in man and mammals, over the developing brain iu the 

 occipital segment only. 



Anteriorly the representatives of the laminae take on a very 

 different disposition. During development the skull, whose long 

 axis was originally a direct continuation of, and in the same plane as, 

 the vertebral column, becomes at an early period bent, or, as it is 

 usually described, flexed downwards. One of the important results 

 of this flexion is the dissociation of the anterior portion of the lateral 



Fi-. I. 



EC 



A diagram to represent the disposition of parts in tliebase of the primitive stull. 



N.C, Notochord; Fa, parachordals ; P.C, periotic capsules; T, trabeculse; 

 C.T, elLmo-Tomerine region. 



neural walls from the parts immediately adjacent. Eventually 

 these dismembered portions of the neural walls coalesce around the 

 down-bent brain and are recognized as the trabeculse cranii. This 

 admirable explanatiouwas first promulgated by Goette (Entwicklung- 

 geschichte der Unke, page 629) ; and this view has certainly much 

 more to recommend it than the notion that the trabeculse are to be 

 regarded as a pair of branchial arches. 



1 Vide Huxley, " The Cranio-facial Apparatus of Petromyzon" Journal 

 Anatomy and Physiolog.v, vol. x. p. 418. 



