364 Bashford Dean Memorial Volume 



NOTOCHORD AND VERTEBRAL COLUMN 



In Chlamydoselachus, the notochord is persistent to a degree not found in the higher 

 elasmobranchs. Perhaps in no other Hving shark does the notochord of the adult retain 

 its primitive condition through so large a portion of its length. The notochord of Chlamy- 

 doselachus extends from the pituitary fossa of the basis cranii to the extreme tip of the 

 tail. In the basis cranii it is very slender, but elsewhere it is a fairly stout rod. 



ii. 



-fci, v.f. s.li. 3..f. s.<i.X. 



ci. '^^- i 4 





c.i.s 



rh<, 



Text'figure 30. 



Vertical longitudinal section of the anterior end of the vertebral column in a large female 



Chlamydoselachus, showing calcified cyclospondylous centra. 



bd., basidorsal; ca!., calcification; ex. 5, cyclospondylous centrum of the fifth cervical vertebra; ch., notochord; 

 ch.s., chordal sheath; d./., dorsal root foramen; i.d., interdorsal cartilaginous element; s.bd., suprabasidorsal; 

 s.d.L, supradorsal Hgament; soA, spino-occipital foramen; v.f., ventral root foramen; X, foramen for tenth 



cranial nerve. 

 After Goodey, 1910.1, Fig. 10, pi. XLIII. 



In the cervical (cephaHc, according to Goodey's nomenclature) and main caudal 

 regions the notochord of Chlamydoselachus shows pronounced metameric constrictions 

 (Text-figures 29, 30 and 31) due to inward projecting thickenings of its sheath. In the 

 trunk region and in the region of the dorsal and anal fins, the constrictions of the noto- 

 chord are very slight (Text-figures 32 and 33); according to Garman (1885.2, Fig. 2, pi. X) 

 they are limited to the ventral portion of the notochordal sheath and do not extend to 

 the notochord proper. The metameric constrictions of the notochord are of interest 

 because they occur in connection with the formation of rudimentary cyclospondylous 

 centra. In Chlamydoselachus we find initial stages in the formation of these centra. 



Similar constrictions of the notochord occur in Heptanchus. For the cervical region 

 and near the base of the anal fin, these are illustrated by Text-figures 34 and 35. In the 

 trunk region of Heptanchu^ the constrictions of the notochord are sUght (Daniel, 1934, p. 

 48). In Hexanchus (Regan, 1906.2, p. 740) the notochord is constricted by annular 

 thickenings of the cartilaginous sheath, without calcification such as occurs in Hepta- 

 branchias (Heptanchus) where the notochord is constricted vertebrally by a series of 

 calcified rings. 



On page 351 I have described the continuity of the vertebral portion of the notochord 

 with its more slender portion imbedded in the cranium. All observers agree in empha- 

 sizing the firmness of the attachment of the vertebral column to the cranium. Goodey 



