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RHYNCHOCEPHALIA

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Originally appearing in Volume V23, Page 142 of the 1911 Encyclopedia Britannica.

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RHYNCHOCEPHALIA . II. The quadrate See also:

BONE (a word common in various forms to Teutonic languages, in many of which it is confined to the shank of the leg, as in the German Bein)
BONE, HENRY (1755-1834)

bone loosely articulated to the cranium and at the proximal end only (Streptostylica). No distinct supramastoid, nor opisthotic; one or no See also:

POST

post-orbital See also:

bar; scapular See also:

arch, when See also:

PRESENT

present, See also:

EXTERNAL

external to ribs; ribs one-headed. See also:

Order 12, SQUAMATA. While this See also:

CLASSIFICATION (Lat. classis, a class, probably from the root cal-, cla-, as in Gr. icaMce, clamor)

classification was being considered and prepared, both See also:

Cope and G. See also:

BAUR, FERDINAND CHRISTIAN (1792-1860)

Baur made a See also:

SPECIAL

special study of the bones which surround the quadrate and arch over the biting muscles in the various See also:

groups of See also:

REPTILES (Lat. Reptilia, creeping things, from reptilis; ref ere, to creep; Gr. Ep7rety, whence the term " herpetology," for the science dealing with them)

reptiles. This led to a See also:

SERIES (a Latin word from serere, to join)

series of discussions which ended in the See also:

IDEA (Gr. Ibia, connected with i&eiv, to see; cf. Lat. species from specere, to look at)

idea, that the class could be most naturally divided into two See also:

GREAT

great subclasses, the one culminating in tortoises and mammals, the other in crocodiles, lizards, See also:

SNAKES

snakes and birds. See also:

PROFESSOR (the Latin noun formed from the verb profiteri, to declare publicly, to acknowledge, profess)

Professor H. F. See also:

OSBORN, SHERARD (1822—1875)

OSBORN in 1903 8 therefore proposed the following classification:— Osborn. Subclass SYNAPSIDA.

Primarily with single or undivided temporal See also:

ARCHES, COURT OF

arches. Giving rise to the mammals through some unknown member of the Anomodontia. Orders Cotylosauria, Anomodontia, Testudinata and Sauropterygia. Subclass DIAPSIDA. Primarily with See also:

double or divided temporal arches. Giving rise to the birds through some unknown type transitional between Protorosauria and Dinosauria. Orders Dinptosauria (=Protorosauria, Pelycosauria and Rhynchocephalia), Phytosauria (=Belodon, &c.), Ichthyosauria, Crocodilia, Dinosauria, Squamata and Pterosauria. The most exhaustive and See also:

MODERN

modern See also:

general See also:

WORK

work on reptiles is by Dr C. K. See also:

HOFFMANN in See also:

BRONN, HEINRICH GEORG (1800-1862)

Bronn's Klassen and Ordnungen See also:

des Thierreichs (1879-90). A most useful and less technical !f°tt See also:

TREATISE

treatise is the See also:

VOLUME

volume on See also:

AMPHIBIA

Amphibia and Reptiles contri- buted by Dr H. Gadow to the See also:

Cambridge Natural See also:

HISTORY

History mane.

(See also:

LONDON

London, 1902). (A. C. G.; A. S. Wo.) II. GENERAL CHARACTERS OF THE CLASS REPTILIA Reptiles, as known in the existing See also:

WORLD

world, are the modified, and in many respects degenerate, representatives of a See also:

GROUP

group of See also:

LUNG

lung-breathing vertebrate animals which attained its maximum development in the Mesozoic See also:

period. So far as can be judged from the See also:

SKELETON

skeleton, some of the members of this group then living might have become mammals by very slight See also:

CHANGE (derived through the Fr. from the Late Lat. cambium, cambiare, to barter; the ultimate derivation is probably from the root which appears in the Gr. «a urmu', to bend)

change, while others might as readily have evolved into birds. It is therefore probable that the class Reptilia, as now understood, comprises the See also:

DIRECT

direct ancestors both of the See also:

MAMMALIA (from Lat. mamma, a teat or breast)

Mammalia and Aves. Assuming that its See also:

EXTINCT

extinct members, which are known only by skeletons, were organized essentially like its existing representatives, the class ranks higher than that of the lowest five-toed vertebrates (class See also:

BATRACHIA

Batrachia) in the investment of the foetus by two membranous envelopes (the amnion and allantois), and in the See also:

TOTAL

total See also:

ABSENCE (Lat. absentia)

absence of gills even in the earliest embryos. It ranks below both the Mammalia and Aves in the partial mixture of the arterial See also:

BLOOD

blood with the venous blood as it leaves the See also:

heart, thus causing the organism to be See also:

COLD (in O. Eng. cald and ceald, a word coming ultimately from a root cognate with the Lat. gelu, gelidus, and common in the Teutonic languages, which usually have two distinct forms for the substantive and the adjective, cf. Ger. Kolte, kalt, Dutch koude

cold-blooded; it also differs both from Mammalia and Aves in retaining a -pair of aortic arches, of which only the See also:

LEFT

left remains in the former, while the right one is retained in the latter. No feature in the endoskeleton is absolutely distinctive, except possibly the degeneration of the parasphenoid bone, which separates the Reptilia from the Amphibia.

In the exoskeleton, however, the epidermis forms horny scales, such as never occur in Amphibia, while there are no traces of any structures resembling either hairs or feathers, which respectively characterize Mammalia and Avds. There is little doubt that true reptiles date back to the latter See also:

PART

part of the Palaeozoic period, but at that See also:

EPOCH (Gr. E7roxij, holding in suspense, a pause, from E1rxav, to hold up, to stop)

epoch the Amphibia approached them so closely in the characters of the skeleton that it is difficult to distinguish the members of the two classes among the fossils. Some of the Palaeozoic Amphibia—a few of the so-called Labyrinthodonts—are proved to have had well-See also:

DEVELOPED

developed gill-arches in their immature See also:

state, while there are conspicuous marks of slime-canals on their skulls. Others are , Mein. See also:

AMERICAN

American See also:

Mus. Nat. Hist. (See also:

NOVEMBER (Lat. novem, nine)

November 1903), vol. i. See also:

art. viii. merely regarded as Amphibia because they closely resemble the genera which are proved to have been gill-breathers when immature. All these genera, however, so far as known, agree with the existing Amphibia in the See also:

PRODUCTION (Lat. productionem, from producere, to pro-duce)

production of their large parasphenoid bone as far forwards as the vomers to See also:

FORM (Lat. forma)

form a rigid and See also:

COMPLETE

complete basicranial See also:

AXIS (Lat. for " axle ")

axis (fig. r, A). Those genera which less resemble the typical Labyrinthodonts are characterized by the reduction of the parasphenoid bone so that it no longer reaches the vomers; in these animals the weakened See also:

SKULL

skull exhibits a secondary basicranial axis formed by the approximation of the. pterygoids to the median See also:

LINE

line (fig. I, B).

The latter See also:

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

condition is universal in existing reptiles, and may there-fore perhaps be regarded as a diagnostic feature. If so, the See also:

OLDEST

oldest known undoubted reptile is Palaeohatteria, from the See also:

LOWER

Lower See also:

PERMIAN

Permian of See also:

Saxony. In the structure of the skull Palaeohatteria is much like the existing See also:

SPHENODON, or TUATARA

Sphenodon, the cheek-plates which See also:

COVER (from the Fr. convert, from couvrir, to cover, Lat. cooperire)

cover the temporal and masseter muscles on each See also:

side being pierced by two great vacuities, one See also:

SUPERIOR

superior-temporal, the other lateral-temporal. The See also:

MAJORITY (Fr. majorite; Med. Lat. majoritas; Lat. major, greater)

majority of the earliest reptiles, however, either resemble the Labyrinthodonts in having the biting muscles completely covered with a roof of bony plates, or exhibit a slight shrinkage of this investment so that a superior-temporal vacuity appears. As the various groups or orders become differentiated, this shrinkage or reduction continues, while the shape of the ossifying See also:

EAR (common Teut.; O.E. are, Ger. Ohr, Du. oor, akin to Lat. auris, Gr. ovs)

ear-See also:

CAPSULE (from the Lat. capsula, a small box)

capsule changes, and the squamosal bone, which covers the See also:

ORGAN

organ of See also:

HEARING (formed from the verb " to hear," O. Eng. hyran, heron, &c., a common Teutonic verb; cf. Ger. Koren, Dutch hooren, &c.; the O. Tent. form is seen in Goth. hausjan; the initial h makes any connexion with " ear," Lat. audire, or Gr. &Kobew very doub

hearing in the fishes, and presumably also in the Palaeozoic Batrachia, is gradually thrust outwards from all connexion with this capsule except at its hinder See also:

ANGLE (from the Lat. angulus, a corner, a diminutive, of which the primitive form, angus, does not occur in Latin; cognate are the Lat. angere, to compress into a bend or to strangle, and the Gr. ayKOS, a bend; both connected with the Aryan root ank-, to

angle. The resultant modifications are diagrammatically represented in fig 2. In one series of orders, comprising the Anomodontia, Chelonia, Sauropterygia and Ichthyopterygia (fig. 2, B, C), the superior-temporal vacuity (s) first appears, and the cheek-plates in the broad temporal arch thus formed may be variously fused together, sometimes even irregularly perforated—showing at first, indeed, the usual inconstancy of a new and not completely established feature. From the earliest members of this series of reptiles, palaeontology seems to demonstrate that the Mammalia (with one robust temporal See also:

ARCADE

arcade or zygomatic arch) arose. In a second series, comprising the orders Rhynchocephalia, Dinosauria, Crocodilia and Ornithosauria (fig. 2, D), the broad arch of cheek-plates is regularly pierced by a lateral-temporal vacuity, which leaves a narrow bar above, another narrow bar below, and uncovers the See also:

MIDDLE

middle part of the quadrate bone. By the See also:

CONSTANT, BENJAMIN (1845-1902)

constant loss of the lower, and the frequent lossof the upper, bar, some members of this series eventually pass into the order Squamata (Lacertilia+Ophidia), in which the quadrate bone is completely exposed and loosely attached to the skull (fig.

2, E); other reptiles exhibiting a similar modification may readily have acquired the typical Avian skull (fig. 2, F) by the loss of the upper and the retention of the lower temporal bar in question.

End of Article: RHYNCHOCEPHALIA

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