1916] 



Daniel: The Aiiatiiinjj nf Ileptaiivhus maciiluhis 



;559 



A sagittal section throiigli the eoliimii of this region shows the 

 finer internal structures of the segments (text-fig. E). In this the 

 plates of the neural arch are regularly arranged and need no further 

 description. The central part of the column offers great simplicity. 

 It consists largely of the notochordal sheath (sh.), around which is a 

 thin layer of cartilage. The sheath is slightly thicker dorsally than 

 ventrally and has the appcariincc of being transversed by iiniltitiides 



bd. ii s,M (d l» 





Fig. D. Segments 5-10 spinal column, Hiptinicliiis maculatiit! (xl). 

 Fig. E. Sagittal section segments .5-10 spinal column, Heptanchug maru- 

 latus (x 1). 



56 1»!<J 



Fig. F. Lateral view of transitional area of column, Heptaiichns inurKhitits, 

 viewed as a transparent object. 



bd., basidorsal plate; bv., basiventral plate; c, central column; chd., noto- 

 chord; f.d., foramen for dorsal root of nerve; f.v., foramen for ventral root of 

 uerve; h.a., haemal arch; id., interdorsal plate; I'l'., interventral plate; m., 

 median lighter zone; n.c, neural canal; )■., rib; .■••., septum, s.hd., suprabasidor.sal 

 cartilage; sh., sheath of notochord. 



of fibers. A tissue much lighter in color (wi.) lies within this and 

 passes inward, causing a constriction of the central notochord, the 

 constrictions being much more pronounced ventrally than dorsally. 

 In a specimen nine feet in length these constrictions of the notochord 

 formed a series of septa (s.) like the nodes of a plant. In this, how- 

 ever, the septa had passed from the ventral wall almost completely to 

 the dorsal and were so thin as to be transparent. 



In the ventral part of these septa (Hasse, 1882) described for 77. 

 cinereus a considerable amount of calcification. It has long been 

 recognized that in this regard Eeptanclius cinereus is even more 



