270 REPORT — 1S46. 



vie arch resuming its primitive unity, and with fewer joints than in lepidosiren, 

 but manifesting the principle of vegetative repetition by a bifurcation of the 

 distal segments. Such is its form in the Proteus anguinus and in the Amphi- 

 uma didactylum : in another species of amphiume, the radiated type is more 

 strongly marked by the subdivision of the last segment into three rays, the 

 homology of which with certain of the five terminal rays, called toes or 

 digits in the human foot, is signified by Cuvier's specific name ' tridactylum' 

 applied to this species ; the middle segment of the appendage is bifid, the 

 first one is undivided. In the menopome (fig. 28), the proximal segment 

 (05) is likewise single, the second segment (66, 67) double, and a mass of carti- 

 lage (68) separates this from the last segment which branches into five, jointed 

 rays (ett). In the frog two styliform bones are developed in the position of 

 the cartilage (es in fig. 27), forming a fourth segment of the division : they 

 are replaced by more numerous and shorter bones in higher vertebrates, in 

 which it will be unnecessary to pursue the metamorphoses of the appendage 

 as it is adapted for swimming, steering, balancing and anchoring, for explora- 

 tion, for burrowing, creeping, walking and running, for leaping, seizing, 

 climbing, or sustaining erect the entire frame of the animal. Its parts under 

 these endless and extreme modifications have necessarily received special 

 names : the first segment (55) is the thigh, femur ; the second is the leg, and 

 its two rays or bones are called tibia (66) and Jibula (67) : the segment (es) 

 is called ankle or tarsus, each of its component ossicles having its proper 

 name ; and the last radiated segment (69) includes the metatarsus and pha- 

 langes : the segments 6s and 69 are termed collectively, the foot, pes*. 



The primitive function of the simple diverging appendages (fig. 17, a, a) 

 of the abdominal vertebra? in fishes is closely analogous to that of the more 

 developed appendage of the pelvic vertebra, viz. to aid in locomotion, as 

 fulcra to the muscles concerned in that act. In crocodiles and birds they 

 serve to connect one costal arch with the next arch in succession, associating 

 them in action or giving fixity and strength to the whole thoracic cage. 



Any given appendage might, however, have been the seat of such develop- 

 ments as convert that of the pelvic arch into a locomotive limb : and the true 

 insight into the general homology of limbs leads us to recognise many poten- 

 tial pairs in the typical endo-skeleton. The possible and conceivable modi- 

 fications of the vertebrate archetype are far from having been exhausted in 

 the forms that have hitherto been recognised, from the primaeval fishes of 

 the palaeozoic ocean of this planet up to the present time. 



The beneficent Author of all, who has created other revolving orbs, with 

 relations to the central source of heat and light like our own, may have willed 

 that these also should be the seat of sentient beings, suited to all the condi- 

 tions of animal enjoyment existing in such planets ; basking, perhaps, in the 

 solar beams by day, or disporting in the soft reflected light of their earth's 

 satellites by night. The eyes of such creatures, the laws of light being the 

 same, would doubtless be organized on the same dioptric principles as ours ; 

 and, if the vertebral column should there, as here, have been adopted as the 

 basis of the higher animal forms, it may be subject to modifications issuing 

 in forms such as this planet has never witnessed, and which can only be con- 

 ceived by him who has penetrated the mystery of the vertebrate archetype, 

 and recognised the kind and mode and extent of its modifications here. 



It is, for example, by no means essential to that organic type that it should 

 be 'tetrapodal' : although it best accords with the force of attraction and other 



* A remarkable example of the extent to which an early or low form of such segment 

 may be regained by adnormal development in a higher species is given by Kerkringius, 

 Opera Omnia, 4to. 1717, p. 55, tab. viii. 



