Page:Encyclopædia Britannica, Ninth Edition, v. 1.djvu/806

Rh 7G2 AMPHIBIA The Salamandrida usually have seven carpal elements. In the proximal row there are two a radiale and a coalesced intermedium and ulnare. There is a single centrale and four distalia. These are variously ossified until, in Triton cristatus and alpcstris,a are ossified. No urodele amphibian has more than four digits in the manus, and the number may be reduced to three, or even two (Amphiuma didactylum}. When four digits are present the number of the phalanges is usually 2, 2, 3, 2. Among the Anura, Duges and Gegenbaur have shown that Bom- binator and Pelobates have eight distinct carpal bones two in the proximal row (radiale, intermedium-uluare), five in the distal, and one between these two rows. This last, which is the centrale, lies on the radial side of the manus, and articulates with the three radial distalia, much as the navicular bone articulates with the three cuneiforraia in the mammalian tarsus. In Rana esculcnta, there are also two bones in the proximal row, and the ceutrale lies on the radial side of the carpus. But there are only three bones in the distal row ; one large, on the ulnar side, which bears the third, fourth, and fifth metacarpals, and two small ossicles on the radial side, which articulate with the first and second metacarpals. There are five digits in the manus of the Anura ; but the pollex is rudimentary, being represented only by a cartilaginous or more or less ossified style. The second and third digits usually have two phalanges each, and the fourth and fifth, three (2, 2, 3, 3). The pectoral arch of the Labyrinthodonts is best known in Archegosaurus, where it presents three ossified elements, which pro bably answer to the coracoid, pracoracoid, and scapula. The bones of the fore-limb in the Labyrinthodonts are always weak relatively to the size of the body. There appear to have been five digits, the carpus remaining unossified. In Proteus, Mcnobranchus, and Amphiuma, the pelvic arch is not connected with any distinctly modified sacral vertebra, and the ilium is very small. The pubes and ischia are represented by broad cartilaginous plates, which unite, and may become fused together in the middle line. In Mcnobranchus, the pubic portion of the pelvis is continued for wards into a broad triangular median process. In Siredon, Meno- poma, Crypiobranchus, and the Salamanders, there is a similar median process, reminding one of the omosternum in the pectoral arch of the Anura. It becomes bifurcated anteriorly. The ilium is always ossified ; and there are ischial ossifications in all but Proteus. On the other hand, the pubic region always remains cartilaginous in the Urodcla. Hyrtl has shown that Cryptobranchus has no proper knee-joint, the femur being united with the tibia and fibula by a solid fibrous mass ; and that, in Menopoma, the cavity of the knee-joint is very small. The tibia and fibula in the Urodcla are always separate, and the proximal elements of the tarsus are not elongated. The greatest number of tarsal elements is found in Cryptobranchus and Mcno poma, which, according to Hyrtl, have three cartilages in the proxi mal, and five in ths distal, row, while two are central. In Siredon, the tarsus completely resembles the carpus, but there is one more distal cartilage. The tarsus therefore consists of three proximal cartilages (tibiale, intermedium, fibulare), one central (centrale}, and five distal (distalia). In the Salamanders, there is usually the same number and disposition of the tarsal cartilages ; but more or fewer are ossified, and it is interesting to remark that the two fibular distalia sometimes become united into a &quot;cuboid.&quot; Menobranchus has two (or three) proximal, one central, and three distal tarsal cartilages ; Amphiuma, three proximal and two distal ; Proteus, two cartilages on the fibular, and one on the tibial side. Siredon, Cryptobranchus, Mcnopoma, and most Salamanders have five digits in the pes ; Mcnobranchus, four ; Amphiuma, three ; and Proteus, two. The number of the phalanges in the pentadactyle foot is usually 2, 2, 3, 3, 2. In Siredon, Hyrtl found 1, 2, 3, 4, 2. In the Anura, the ilium is greatly elongated, and the pubes and ischia are flattened, discoidal, and applied together by their inner surfaces. The ilium and the ischium, alone, become completely ossified, and there is no prapubic process. The tibia and fibula coalesce into one bone. Two elongated bones form a proximal row in the tarsus, and are commonly united by their epiphysial ends (e.g., Rana; they remain separate in Bom- binalor). In Rana esculenta, the distal confluent ends of these bones (which possibly answer to the astragalus and calcaneum) pre sent a transversely elongated articular surface, which is convex from the dorsal to the plantar side. Between this and the proximal end of the second and third metatarsals lies a discoidal, more or less calcified, cartilage. The convex distal face of this cartilage articu lates with these two metatarsals. From its fibular side a strong ligamentous band passes to the proximal end of the fifth metatarsal, and a fibrous plate to the fibular and plantar edge of the fourth metatarsal, so that the band and plate are interposed between these metatarsals and the coalesced astragalus and calcaneum. On the tibial side of the discoidal cartilage lies another, which is elongated from the dorsal to the plantar side, and concave proximally, to articulate with the tibial side of the distal end of the coalesced astragalus and calcaneum The inner or tibial face of this cartilage articulates with the proximal end of the elongated first joint of th calcar. Its distal end is connected by a strong band of ligamentoua fibres, within which a nodule of cartilage may be enclosed, with the proximal ends of the first and second metatarsals. The second joint of the calcar has the form of an ungual phalanx. InJSufo and Bombinator, according to Gegenbaur, the calcar con sists of only a single piece. The pelvic arch of the Labyrinthodonts appears to have contained a well-ossified pubic element, in which respect it differs from that of all other Amphibia. The hind-limb, like the fure-limb, was relatively weak. The tibia and fibula are distinct. In the few cases in which the pes is preserved it is pentadactyle, with a short cartilaginous tarsus. The Integumentary Organs. In all recent Amphibia, the integu ment is remarkable for the great abundance of simple follicular glands which are distributed through it, and are sometimes all of one kind (e-.g., Proteus), though in other cases two sorts of such glands can be distinguished (Rana}. In many Anura and Urodcla, these glandular structures attain a greater complication of structure, especially near the angle of the jaw, and constitute what are termed the &quot; parotoid &quot; glands. In some cases, the secretion of these glands is extremely acrid and irritating. In some Urodcla (Proteus and Siredon}, and in the tadpole, the epidermis becomes modified in relation with the termination of sensory nerves, in the head and along the body, in the region of the nerve of the lateral line, and gives rise to sensory organs of the same nature as those which are found in the lateral line and the so-called mucous sacs and canals of fishes. 1 In a few Anura, ossification takes place in the dorsal integument, and this process may go so far as to give rise to bony plates, which may become closely connected with the spines of the subjacent vertebral (Brachycephalus, Ceratophrys). In the majority of the Peromda, oval, cycloid scales are imbedded in the transverse folds of the integument, and constitute another point of resemblance be tween the members of this group and the Labyrinthodonts. But the rows of scales are not confined to the ventral surface, and the scales themselves differ in structure from those of the Labyrinthodonts. In the Urodela and Anura, the epidermis is periodically exuvi ated. The Alimentary Organs. The teeth of the recent Amphibia vary a good deal in form. In the Urodela, they are usually conical and pointed ; frequently more or less curved ; some times, as in Anaides, lancet-shaped. Siren has the surfaces of the vomers and palatines covered with parallel series of small dents en brosse. In Ceratophrys, the bases of the teeth are slightly grooved longitudinally. In Archego saurus, similar grooves are more marked, and give rise to folds of the wall of the tooth. These, extending inwards and ramifying, give rise to the complicated or &quot; labyrin- thic&quot; structure exhibited by transverse sections of the teeth of the typical Labyrinthodonts. Very generally, the teeth become ankylosed with the subjacent bones, and are replaced by others developed at their bases. In the Laby rinthodonts, some of the anterior teeth frequently become much larger than the rest. The Anura are remarkable for the total absence of teeth in the mandibles, in all but one or two genera, while many have no premaxillary or maxillary teeth. The Toads have no teeth in the upper jaw. Pipa is altogether edentulous. Siren alone presents plates of horn upon the gingivel surfaces of the premaxillie and of the dentary elements of the mandible. Teeth may be developed upon the prcmaxillae and maxillie, the palatines, and the dentary and the splcnial elements of the mandible; but they do not occur else where, the so-called sphcnoidal teeth of some Salaman ders being really borne, as has been seen, on the peculiarly modified palatines. The buccal cavity is usually spacious, and the widely-separated posterior nares open into the anterior part of it. In the lower Uro dcla, the branchial clefts lie at the sides of the pharynx, and the median aperture of the glottis is situated far back. In the Urodcla, and some Anura, there are no Eustachian passages ; but, in most Anura, these passages have the form of wide recesses leading out of the pharynx. In Pipa and Dactylethra alone, the &quot;recesses&quot; are converted into Eustachian &quot;tubes,&quot; which open by a common 1 Rechcrches sur les organs sensitifs, qui se (rouvent dans Ttpidcrmt du Protec et de I Axolotl, by E. Bugnion. Lausanne, 1873.