. On the anatomy of vertebrates [electronic resource] . fibrous bands, diverging from the notochord, and givingthe first indication of the segmental character of the skeleton. In Dermopteri the neu- adipose substance ral and haemal canals are /^--^formed by a separation of inner layer -mk the layers of the outerdivision of the sheath of the notochord fi° 22 .A. [ransverse vertica* section of vertebral column of Myxine. xxj. transverse partition divides the larger portion of the neural canal,lodging the myelon, from a smaller portion above containingadipose tissue. In the Lancelet the substance
. On the anatomy of vertebrates [electronic resource] . fibrous bands, diverging from the notochord, and givingthe first indication of the segmental character of the skeleton. In Dermopteri the neu- adipose substance ral and haemal canals are /^--^formed by a separation of inner layer -mk the layers of the outerdivision of the sheath of the notochord fi° 22 .A. [ransverse vertica* section of vertebral column of Myxine. xxj. transverse partition divides the larger portion of the neural canal,lodging the myelon, from a smaller portion above containingadipose tissue. In the Lancelet the substance of the noto-chord, fig. 23, ch, consists of a number of circular discoidor flattened vesicles, pressed one upon another within thesheath, like a pile of coins in a purse ; the sheath is strength-ened by a longitudinal filamentary ligament above and septa pass off, with each pair of nerves, to theinterspaces of the muscular segments, giving attachments tothe fibres. A median vertical membrane rises from the neural 23 h Jij^jJ oA md. Diagram of anatomy of the Lancelot, Brcmchiostoma sheath, and beyond the abdominal cavity descends from the hreinalsheath, passing between the right and left series of dermo-neural and dermo-haamal spines are indicated by shortlinear series of firmly adhering flattened cylindrical cells. Thenext step in the skeletal tissues is shown in a pair of jointedcartilaginous filaments, fig. 23, h, which bound or strengthen theborders of the longitudinal oral slit, each cartilage supporting onconical prominences the oral cirri (ib. f, f): numerous carti-laginous filaments strengthen the sides of the branchial cavity, , with intervening fissures, not opening upon the skin. In theLamprey cartilaginous neurapophyses, fig. 24, n, n, strengthen thesides of the neural canal. In the Sturgeon, fig. 25, the inner 32 ANATOMY OF VERTEBRATES. layer of the notochordal capsule has assumed the texture of toughhyaline cartilage; and not
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