94 



AMPHIBIA. 



verse processes are only found on a few of the 

 most anterior vertebra. 



The spine of the proteus is not sufficiently 

 different from that of the siren to require any 

 particular description. 



The construction of the members, both an- 

 terior and posterior, especially the latter, will 

 be found to be arranged on very different plans, 

 according to the habits and requirements of the 

 different groups, and particularly their mode of 

 progression. In the apoda, as the cacilia, there 

 are not even the rudiments of limbs. In the 

 other orders they exist under very different 

 degrees of development, according as they are 

 constructed for leaping and swimming, as in 

 the frogs, toads, &c., or for creeping, as in the 

 salamanders ; or they are rudimentary, and 

 without any very apparent use, as in the am- 

 phiuma. It will be necessary to give a cursory 

 description of these forms. 



Of the anterior extremity in the anoura. 

 The shoulder of the frog (jig. 16, f. Jig. 17.) 

 consists of the scapula, the clavicle, and the 

 coracoid bone, which all combine to form the 

 glenoid cavity for the head of the humerus. 

 The scapula is composed of two very distinct 

 portions. The upper, (Jig. 17, a,) which is 



Fig. 17. 



permanently cartilaginous, at least at its mar- 

 gin, is articulated moveably to the inferior and 

 more solidly ossified piece, (Jig. 17, b,) at the 

 inferior and posterior part of which is the arti- 

 cular surface forming its portion of the glenoid 

 cavity, immediately anterior to which it is at- 

 tached to the clavicle. (Jig- 17, c.) This 

 bone is slender and straight, and is connected 

 beneath with its fellow in the median line. 

 The coracoid bone (fig. 17, d) is considerably 

 larger than the clavicle, and is also connected 

 with its fellow by its broad median margin. 

 The sternum consists of several pieces, ex- 

 tending from before the clavicles to some dis- 

 tance behind the coracoid bones; the latter 

 terminates in a broad xiphoid cartilage. These 

 parts differ considerably in their relative pro- 

 portions in different genera. 



The arm is developed in a very inferior de- 

 gree compared with the hinder extremity. The 

 humerus (Jig. 17, g) is short and thick, having 

 a rounded head, received into the glenoid ca- 



vity of the shoulder-joint. The opposite extre- 

 mity forms an almost globular surface for its 

 articulation with the bone of the fore-arm, 

 which is still shorter, and consists of the radius 

 and ulna united, (fig. 17, li,) having only a 

 slight groove to show their line of union. The 

 carpal bones (jig- 16, i) are six in number, 

 supporting the four metacarpal bones, (Jig. 16, 

 k.) The index and middle finger have each 

 two phalanges, the others three. The index is 

 particularly large in the male. The thumb is 

 merely rudimentary. 



The posterior extremity is greatly developed 

 in the frogs, for the purpose before mentioned, 

 of enabling them to take long leaps, and to 

 swim with great rapidity and energy. The 

 pelvis consists of the three essential bones of 

 this part, the ilium, ischium, and pubis on 

 each side. The iliac bones, (jig. 16, d,) di- 

 verging above, are moveably articulated with 

 the sacrum. They then extend backwards, and 

 form, together with the small ischiatic and pubic 

 bones, (jig- 16, I,) the cotyloid cavities for the 

 reception of the femur. This bone (fig. 16, m) 

 is nearly twice as long as the humerus, cylin- 

 drical, and having a slight double curve. 

 The leg consists, like the fore-arm, of but one 

 bone, the tibia and fibula being anchylosed 

 through their whole length. This bone (fig. 16, 

 n) is even a little longer than the femur. It 

 is succeeded by two bones of considerable 

 length, (fig. 16, o,) having very much the 

 aspect of a tibia and fibula, but which must 

 be considered as bones of the tarsus greatly 

 modified, and are most probably the us culcis 

 and the astragalus. Between these elongated 

 bones and the metatarsal are four small tarsal 

 bones. The metatarsal bones (Jig- 16, p) are 

 much elongated, as are also the phalanges, 

 (fig. 16, q,) for the purpose of forming strong 

 oars or paddles with the intervention of a broad 

 web of integument. The inner toe is consi- 

 derably developed, and the whole structure of 

 the foot and leg thus combines to furnish a pow- 

 erful and efficient organ of progression. 



The elongated forms of the aquatic sala- 

 mander, the proteus, the siren, &c., in which 

 the vertebrae are developed to so great an extent, 

 present the opposite extreme in the structure of 

 their limbs. These are small, feeble, and ap- 

 pear as it were abortions. In the genus triton 

 and in the salamandra, which possess both an- 

 terior and posterior extremities, they differ but 

 little in their general form and development. 

 The bones of the fore-arm as well as of the leg, 

 instead of being respectively anchylosed into 

 a single piece, as in the frogs, are permanently 

 separate, consisting of a distinct ulna and radius 

 in the former, and an equally distinct tibia and 

 fibula in the latter. The toes are four, both 

 before and behind ; they are short, slender, 

 and of slight construction. 



This imperfect development of the extremi- 

 ties is, however, as we have seen, admirably 

 compensated by the extraordinary extent of the 

 spine both in the body and the tail ; and while 

 the limbs afford but very imperfect means of 

 progression on land, the structure of the spine 



