A treatise on zoology . A CIPENSEROIDEf 315 Sub-Order 2. ACIPENSEROIDEI. According to the researches of Traciuair [-i)!] and A. [505], the families in this group form a degeneratingseries starting from a type simihir to the Palaeoniscids ; they reachtlie highest degree of differentiation in tlie Acipenscrichie. The body remains fusiform with a typical bifurcated hetero-cercal tail. The dorsal and anal fins are moderately short. Theorbits are far forward, near the olfactory capsules, but the snoutbecomes greatly prolonged lieyond them and the mouth. This rostrum is borne by a prolon
A treatise on zoology . A CIPENSEROIDEf 315 Sub-Order 2. ACIPENSEROIDEI. According to the researches of Traciuair [-i)!] and A. [505], the families in this group form a degeneratingseries starting from a type simihir to the Palaeoniscids ; they reachtlie highest degree of differentiation in tlie Acipenscrichie. The body remains fusiform with a typical bifurcated hetero-cercal tail. The dorsal and anal fins are moderately short. Theorbits are far forward, near the olfactory capsules, but the snoutbecomes greatly prolonged lieyond them and the mouth. This rostrum is borne by a prolongation of the median ethmoidcartilage (Fig. iOo). The cartilaginous cranium is, indeed, in livingforms massively developed, and extends far bnclc, passing gradually. Fk;. Left-side view of tin; skull ami vertebral column of Acipcnser. Tlie branchial arches havebeen removed. (From Owen, Antdoini/ of Vcrtebmtcs, by permission of Jlessrs. Longmans andCo.) (I, notochordal sheath ; /; and c, basiventral; c, pleural rib ; d, basidorsal ; (/, inter-dorsal ; e, neural spine ; /, cartilage craiuum; /, anterior neural arches fused on behind ;9t Vt 0i parasplienoid ; y, articulation of hyomandibular; 3, vomerine plate; i, orbit ; /.,nasal capsule; /», hyoniandUiuIar ; », maxilla; j), palatine; s, jugal; 20, pterygoid carti-lage ; 2ii, hyomandibular cartilage ; 2S, symplectic ; 62, dentary. into the vertebral column. Some half-dozen sclerotomes are more orless completely fused with the back of the skull behind the vagus(Sewertzoff [-tOG]); there is no break between the skull and the verte-bral column, and the notochord passes uninterruptedly forwards tothe pituitary region (Fig. 293). The whole cranium is supported below by an immense para-sphenoid, a
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Keywords: ., bookcentury1900, bookdecade1900, bookpublishe, booksubjectzoology
