578 



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



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

 the dorsum sellse — is composed of the same elements as tiie vertehral 

 cohimn, but differs from it in that it has not passed through 

 any stage of vertebi ation ', the notochordal portion with the ])ara- 

 chordals representing the centrum, with the laminae which meet 

 dorsally in man and mammals, over the develojiing brain in the 

 occipital segment only. 



Anteriorly the representatives of the laminae take on a very 

 different dis|)osition. During development the skull, whose long 

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

 the vertehral 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-. 1. 



■EC 



3SI.C 



A diagram to represent the disposition of parts in the base of the primitive skull. 



N.C, Notochord; Pa, parachordals; P.C, periotic capsules; T, trabeculaj; 

 C.T, elhmo-vomerine 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 craiiii. This 

 admirable explanation was first promulgated by Goette (Eutwicklung- 

 geschichte der Unke, page G29) ; and this view has certainly much 

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

 regarded as a pair of branchial arches. 



^ J7c^e Huxley, "The Cranio-facial Apparatus oi Petromyzon" Journal 

 Anatomy and Physiology, vol. x. p. 418, 



