AMPHIBIA. 



AMPHIBIA. 



151 





The vertebral column commences at the posterior part of the head, 

 and, unlike the rest of the Reptiles, the Batrachians, like the rays, the 

 sharks, and the mammiferous animals, possess two condyles situated 

 on the sides of the vertebral hole. In the Tadpole the vertebra; are 

 of the same calibre throughout, but a difference takes place when the 

 limbs are developed. At this period, the vertebral canal diminishes 

 gradually in length, the spinal marrow contracts, and no trace of the 

 canal is left in the elongated coccyx. It is in the Tailless Amphibia 

 that the vertebral column is shortest, for the Frogs have only ten and 

 the Pipas but eight vertebrae. 



As a general rule, the anterior extremities are shorter than the 

 posterior limbs ; but in some of the Frogs especially, the lower 

 extremities are twice or thrice as long as the anterior feet, as might 

 be expected in animals whose progression is principally effected by 

 leaps. Ribs there are none ; but the sternum is highly developed and 

 a large portion is very often 

 cartilaginous. It receives an- 

 teriorly, or in its mesial por- 

 tion, the two clavicles and 

 two coracoids which fit on to 

 the scapula. The whole makes 

 a sort of band which sustains 

 the anterior extremities, and 

 an elongated disk which forms 

 a support for the throat, and 

 assists in the offices of de- 

 glutition and respiration. 

 Another disk extending back- 

 wards, being for the insertion 

 of the recti muscles, protects 

 the abdominal viscera in 

 some species. The pelvis is 

 well developed in the Frogs, 

 especially in the Pipa, and 

 though apparently deprived 

 of all traces of a tail after 

 undergoing their last trans- 

 formation, there remains, in- 

 ternally, a true coccygeal piece, 

 moat frequently even moveable 

 and elongated, but without 

 anything like vertebral form. 



The bone of the humerus or 

 arm is single, and is long in pro- 

 portion to the bones of the fore-arm, which are united throughout their 

 length, their duality being manifested by a simple furrow or depression. 

 These bones are distinct in the reptiles generally, and the radius is 

 generally rather the longest ; the ulna is prolonged backwards into a 

 kind of olecranon, and sometimes this apophysis is distinct, and 

 becomes a sort of sesamoid-bone in the thick part of the tendon of 

 the extensor muscles. The Pipas, the Tortoises, and the greater 

 part of the Sanrians have this conformation. The bones of the carpus, 

 or wrist, exhibit nothing extraordinary in their structure; nor do 

 those of the fingers, which are without nails or claws, require particular 

 notice. 



The bones of the well-developed pelvis present considerable 

 differences jn the various genera of Anourous Amphibia. Thus in the 

 Frogs (Rana) and the Tree-Frogs (Hyla), the ossa ilii are very much 

 elongated, articulated in a moveable manner on the sacrum, and veiy 

 much approximated below towards the cotyloid cavity ; so that the 

 two heads of the thigh-bones seem to be placed in eontact, a 

 conformation which much influences the action of the posterior limbs 

 upon the trunk in the execution of the motions of swimming and 

 ;;. In the Pipa, or Surinam Toad, the ossa ilii are very much 

 widened at the point of junction with the sacrum, which is, itself, 

 dilated, forming a strong union by means of a true symphysis. The 

 femur, or thigh-bone, is very much elongated, and slightly curved in 

 the form of the letter S in the Frogs (Rana), and in the Tree-Frogs 

 i //y/r) / it is a little shorter in the Toads (Bufo), and is flattened in 

 the Pipa. The bones of the leg (tibia and fibula) are, in the Reptiles, 

 illy distinct; but in the Anourous Amphibia, Rana, Jlyla, and 

 /''/"', for instance, they are so soldered together as to form but a 

 single articulation with the femur and tarsus, and to present the 

 appearance of a single very-much-elongated bone, which some have 

 erroneously considered as a supernumerary bone, or second femur. 

 The knee-joint and articulating bones are so disposed that the feet 

 have always a direction outwards. In the Reptiles generally, the 

 posterior feet are more developed than the anterior limbs'; and this 

 modification is particularly observable in the Anouroui Amphibia, which 

 have the tarsus so much elongated as to induce some to consider the 

 first bones composing it to be a fibula or tibia. The bones of the 

 metatarsus correspond to the number of toes. 



The Terth. As these are very important organs in the whole of 

 the Amphibia, we shall now present an abstract of this subject from 

 Professor Owen's celebrated work entitled 'Odontography.' He remarks 

 that the variations which the dental system presents in the A mphibia 

 we more conspicuous in the number, situation, and structure of the 

 teeth, than in their form or mode of attachment. Certain Batrachians, 



Skeleton of the Common Frog. 



he observes, are edentulous, the genus Jfylaplesia among the Tree- 

 Frogs, for example, and the Bufonida;, or Toad Family, with the 

 exception of some species of Bonibinator. The teeth when present 

 ; are described by him as generally numerous, simple, of small and equal 

 size, and close-set, either in a single row or aggregated, like the teeth 

 of a rasp, and he points out a characteristic condition of the dental 

 system in fishes, namely, the absence of teeth ^>n the superior maxillary 

 bone, as being continued in those genera of Perennibranchiate Batra- 

 I chians which stand lowest in the class of Reptiles ; not only the superior 

 \ maxillary teeth, but the bones themselves are absent, he observes, in 

 Siren, Menobranchus, and Proteus. In the Siren, he describes the 

 lower margin of the intermaxillary bones, and the sloping anterior and 

 upper margin of the lower jaw, as trenchant, and each encased in a 

 sheath of firm, albuminous, minutely fibrous tissue, harder than horn. 

 The bones thus armed slide upon each other, he tells us, like the blades 



of a pair of curved scissors, 

 when the mouth is closed, 

 and are well adapted for 

 dividing the bodies of small 

 fish, aquatic larva;, worms, &e. 

 The homy substitute for teeth 

 in the lower jaw is supported 

 by the bony element corre- 

 sponding with the premandi- 

 bular of the Lepidomren. 

 [PROTOPTERUS.] A second 

 bony piece applied to the 

 inner surface of the branch of 

 the jaw (representing the 

 splenial or opercular element 

 in the jaw of the croco- 

 dile) is beset with numerous 

 minute pointed teeth, set in 

 short oblique rows, and di- 

 rected obliquely backwards. 

 The palatal surface of the 

 mouth is described as present- 

 ing on each side two flat, 

 thin, and moderately broad ' 

 bones, forming an apparently 

 single, oblique, oval plate, 

 which converges to meet its 

 fellow at the anterior part of 

 the palate, so as conjointly to 

 constitute a broad rasp-like surface in the form of a chevron. The Pro- 

 fessor regards the anterior long plate on each side as the representative 

 of the divided vomcr, and it supports 6 or 7 oblique rows of small 

 pointed retroverted teeth ; the smaller posterior plate, which he thinks 

 may probably be the homologue of the pterygo'id, is beset with 4 rows 

 of similar teeth ; and thus we have 10 or 11 rows on each side of the 

 chevron of the palate. The greatest number of denticles (11 or 12) 

 is in the middle rows ; in the anterior and posterior rows they are 

 fewer ; all are of similar size and form, corresponding with those of 

 the lower jaw opposed to them. " The condition of the dental system 

 in this, the lowest of the class of reptiles," says Mr. Owen, " is not 

 without interest, independently of the absence of the superior maxillary 

 teeth, and of the presence of the palatal and inferior maxillary dents 

 en carde." If, for example, the dense sheath of the trenchant anterior 

 parts of the upper and lower jaws had been completely calcified and 

 converted into hard dentine, the correspondence between the Siren and 

 the Lepidoiiren would have been very striking in this part of their 

 structure ; but the maxillary sheaths of the Siren being composed of 

 horn, and being moreover easily detached from the subjacent bones, 

 much more closely resemble the deciduous mandibles of the Tadpoles 

 of the higher Batrachians. (Part ii., pp. 188, 189.) 



In the Axolotl also the ichthyic character of the rasp-like teeth are 

 aggregated in numerous rows upon the palatal region of the mouth, 

 and upon the splenial or opercular element of the lower jaw ; but here, 

 Mr. Owen observes, the superior maxillary bones are developed, and 

 support teeth. The premandibular and the intermaxillary bones, he 

 adds, instead of presenting the larval condition of the horny sheath, 

 have their alveolar border armed with a single row of small, equal, 

 fine,- and sharp-pointed denticles, which are continued above along the 

 maxillaries ; thus, he observes, establishing the commencement of the 

 ordinary Batrachian condition of the marginal teeth of the buccal cavity. 

 As in the Siren, the dentigerous bones of the palate consist of two 

 plates on each side ; the anterior pair, or vomers, converge and meet 

 at their anterior extremities, and the minute denticles which they 

 support are arranged quincuncially. The posterior pair of bones 

 continued backwards, according to the usual disposition of the ptery- 

 go'ids, abut against the tympanic or quadrate bones ; and the denticles 

 are coufined to the anterior part of their oral surface, resembling, in 

 their arrangement and anchylosed attachment, those of the palatal 

 series, of which they are the posterior termination. 



The superior maxillaries and their teeth are, it appeal's, wanting in 

 Menobranchus [NECTURCS] ; but in this form an advance to a higher 

 type of dentition is perceptible by the arrangement of the teeth in a 

 single row, both upon the roof and at the margins of the mouth. The 



