The praecaudal portion of the fin-fold on the dorsal side of the body becomes broken into numerous finlets in living Crossopterygians, while in other fishes it disappears throughout part of its length, leaving only one, two or three enlarged portions--the _dorsal_ fins (fig. 4, d.f.). Similarly the praecaudal part of the fin-fold ventrally becomes reduced to a single _anal_ fin (a.f.), occasionally continued backwards by a series of finlets (_Scombridae_). In the sucker-fishes (_Remora_, _Eckeneis_) the anterior dorsal fin is metamorphosed into a sucker by which the creature attaches itself to larger fishes, turtles, &c. [Illustration: From _Cambridge Natural History_, vol. vii., "Fishes, &c.," by permission of Messrs. Macmillan & Co., Ltd. FIG. 4.--_Tilapia dolloi_, a teleostean fish, to illustrate external features. (After Boulenger.) A, Side view. g.r, Gill rakers. B, First branchial arch. l.l, Lateral line organs. a.f, Anal fin. n, Nasal opening. c.f, Caudal fin. p.f, Pelvic fin. d.f, Dorsal fin. p.op, Preoperculum. g.f, Gill lamellae. pt.f, Pectoral fin.] The paired fins--though more recent developments than the median--are yet of very great morphological interest, as in them we are compelled to recognize the homologues of the paired limbs of the higher vertebrates. We accordingly distinguish the two pairs of fins as pectoral or anterior and pelvic ( = "ventral") or posterior. There are two main types of paired fin--the _archipterygial_ type, a paddle-like structure supported by a jointed axis which bears lateral rays and exists in an unmodified form in _Neoceratodus_ alone amongst living fishes, and the _actinopterygial_ type, supported by fine raylike structures as seen in the fins of any ordinary fish. The relatively less efficiency of the archipterygium and its predominance amongst the more ancient forms of fishes point to its being the more archaic of these two types. In the less highly specialized groups of fishes the pectoral fins are close behind the head, the pelvic fins in the region of the cloacal opening. In the more specialized forms the pelvic fins frequently show a more or less extensive shifting towards the head, so that their position is described as thoracic (fig. 4) or jugular (_Gadus_--cod, haddock, &c., fig. 5). [Illustration: FIG. 5.--Burbot (_Lota vulgaris_), with jugular ventral fins.]