The group may be defined as follows: Sessile solitary Coelomata with bivalved shells usually of unequal size and arranged dorso-ventrally.
D.l, Dorso-lumbar, s, sacral, c, caudal vertebrae.
Ilium; Is, ischium; Pb, pubis; d.l, dorso-lumbar vertebrae; Cd, caudal vertebrae; Am, acetabulum.
The next chamber, the urodaeum, is small, and receives in its dorso-lateral wall the ureters and the genital ducts; above and below this chamber is closed by circular folds, the lower of which, towards the ventral side, passes into the coating of the copulatory organ when such is present.
Dorso-lumbar vertebrae never fewer than twentytwo, usually twenty-three in the existing species.
Dpm, Dorso-plastral muscle.
Dv' to dv s, Dorso-ventral muscles (same as the series labelled tsm in fig.
The muscles are composed of outer circular and inner longitudinal layers, and of branched dorso-ventral fibres.
This layer also forms the attachment for the muscles, of which there are two enveloping coats, a circular and a longitudinal layer and also dorso-ventral fibres.
Both head and trunk are somewhat flattened dorso-ventrally, giving the insects a very distinct and characteristic aspect.
The ventral cords are the pedal, the dorso-lateral, the pleural, the former innervating the foot, the latter the mantle.
Growth is greater in the vertical dorso-ventral axis than in the longitudinal oro-anal axis; consequently the foot is relatively small and projects as a blunt process between mouth and anus, which are not widely distant from one another, whilst the antipedal area projects in the form of a great hump or dome.
There are generally nineteen dorso-lumbar vertebrae (thirteen thoracic and six lumbar), the form of which varies in different genera; in the cursorial and leaping species the lumbar transverse processes are generally very long, and in the hares there are large compressed inferior spines, or hypapophyses.
The muscles are striated and arranged in four quadrants, two dorso-lateral and two ventro-lateral, an arrangement which recalls that of the Nematoda, whilst in their histology they somewhat resemble the muscles of the Oligochaeta.
Titanotherium, of the Oligocene of the Dakotas and neighbouring districts, was a huge beast, with the hinder upper premolars similar in character to the molars, a pair of horn-cores, arising from the maxilla, overhanging the nose-cavity, four front and three hind toes, only twenty dorso-lumbar vertebrae, and an almost continuous and unbroken series of teeth, in which the canines are short; the dental formula being i.
Four closed spaces of the nature of body-cavities, two lateral and a dorso-median and a ventromedian.
A.d.l., Anterior dorso-lateral.
P.d.l., Posterior dorso-lateral.
66), at the monastery of Palazzolo; but the position is quite unsuitable for an ancient city, and does not at all answer to Livy's description, ab situ porrectae in dorso urbis Alba longa appellata; and it is much more probable that its site is to be sought on the western side of the lake, where the modern Castel Gandolfo stands, immediately to the north of which the most important part of the archaic necropolis was situated.
The general colour is a delicate pale brown, with about a dozen and a half darker cross-bars, which are often connected by a still darker dorso-lateral streak, enclosing large oval spots.
(a) Integument heavily plated with firm chitinous cuticle, allowing no expansion and retraction of regions of the body nor change of dimensions, except, in some cases, a dorso-ventral bellows movement.
In addition to these three or four circlets of plates, two other elements were once supposed essential to the ideal crinoid: the dorso-central and the oro-central.
- An early stage in the development of Antedon, showing the foot-plate or "dorso-central" fp at the end of the stem col.
Aboral) poles of starfish and crinoids are not comparable with one another, and that all conclusions based on the supposed homology of the dorso-central of echinoids and asteroids with that of crinoids are incorrect.