On the archetype and homologies of the vertebrate skeleton / by Richard Owen.

  • Richard Owen
Date:
1848
Catalogue details

Licence: Public Domain Mark

Credit: On the archetype and homologies of the vertebrate skeleton / by Richard Owen. Source: Wellcome Collection.

Provider: This material has been provided by King’s College London. The original may be consulted at King’s College London.

    208/238 (page 182)
    monly remote position from its proper segment, it may not have been thought i of as a part included in the first class of vertebrae constituting the skull, f Many striking and extreme deviations from the archetype are manifested I in the skeleton of the more aberrant forms of the reptilia. The number off • moveable trunk-segments is reduced to the minimum in the Batrachia (e.g. 7 ’ ' in Pipa), and increased to the maximum in the Ophidia (4-22 in Python),, At first view the principle of vegetative repetition seems to have exliausted I f itself in the long succession of incomplete vertebrae which support the trunk t of the great constrictors: but by the endless combinations and adjustmentsi of the inflections of their long spine the absence of locomotive extremities isi • so compensated that the degraded and mutilated serpent can overreach and , overcome animals of far higher organization than itself: it can outswim the ^ fish, outrun the rat, outclimb the monkey, and outwrestle the tiger; crush- ing the carcase of the great carnivore in the embrace of its redoubled coils, ■ and proving the simple vertebral column to be more effectual in the struggles *• than the most strongly developed fore-limbs with all their exquisite rotatory* mechanism for the effective and varied application of the heavy and formi-* dably armed paws. And whilst the vertebral column of the ophidian order: exhibits the extreme of flexibility, that of the chelonia manifests the opposite, extreme of rigidity : back, loins and pelvis constitute one vast sacrum, or; rather abdominal skull, but a skull suboi’dinated chiefly to the lodgment and defence of a much-developed haemal system, and in which the pleurapophyses, haemapophyses and their spines repeat the same modification of great expan- sion and fixed union by marginal sutures, which the neurapophyses and spines; undergo in the cranium of the higher vertebrates. The well-known deter- mination of the ordinary elements of the typical vertebra in the thoracic-ab- dominal segments of the tortoise need not here be discussed (see pp. 100,* ■ 101) : but it is, perliaps, w'orthj' of repetition that the neurapophyses exhibit the modifieation of cliange of position, like that which has been described in; the sacrum of the bird ; being sliifted from their own centrum over one half of the next eentrum, thus adding to the strength and elasticity of the whole< osseous vault (see p. 95). The confluence of the neurapophysis (14) withi its own moiet}' of the neural sjnne (15) has already been noticed (p. 124) iml tlie anterior segment of tlie ce])halic skull of most chelonia. I may here add that the typical condition of the haemal (maxillary) arch of the sanie segment is well shown in the Etnys expansa. The pleurapojihyses (palatines) meet at the base of the cartilaginous vomer, above and behind the posterior iiares,- sweep outwards and downwards, give attachment to the haemapophyses (maxillaries) which advance and converge, and the arch is closed below the nasal passage by the haemal spine (premaxillary). Cut through the junction of the haemapophyses with the neurapophyses (prefrontals), and with the di- verging appendages (malars), and the inverted arch is then suspended by its proper piers, the pleurapophyses or palatines. In the connation or coalescence of the neurapophyses and spines foiming. the parietal and frontal neural arches in the ophidian and some cheloniau reptiles, we perceive a return to the common constitution of those arches in the vertebrae of the trunk, in which the permanent scparution of the neural spine from the neurapophyses occurs as a rare exception. In the class-skeleton {Aves) represented in fig. 4 the archetype is further departed from than in the typical reptilia; and when the general form of this diagram is contrasted with that of the first figure, the power of demonstrating the fundamental agreement which reigns throughout, and which is equally manifested in the comparison of figure 4 with those of the piscine and rep-