The right ventricle occupies the ventral portion of the heart.
It is protruded and retracted by special muscles which are partly attached to the ventral, distal end of the ilium.
- Syrinx muscles of either side attached to the dorsal and ventral corners of the rings.
The ventral and anal fins are white, tinged with pale red; and the dorsal, pectoral and caudal tipped with black.
The ventral region of the thoracic skeleton is complex, each segment usually possessing a median sternum with paired episterna (in front) and epimera (behind).
The glands occur in groups, and lead into common ducts which open usually so much reduced that the foremost apparent ventral sclerite of the abdomen represents the third sternite.
The well-known "fire-flies" of the tropics are large click-beetles (Elateridae), that emit light from paired spots on the prothorax and from the base of the ventral abdominal region.
A, Male; b, female; c, larva (ventral view).
N 1, Commissure uniting this with ventral ganglion (not shown in fig.).
V.c, Ventral cirrus.
In all Chaetopods this system consists of cerebral ganglia connected by a circumoesophageal commissure with a ventral ganglionated cord.
In the latter, the segmentally arranged ganglia are more sharply marked off from the connectives than in other Chaetopods, where nerve cells exist along the whole ventral chain, though more numerous in segmentally disposed swellings.
The principal trunks consist of a dorsal vessel lying above the gut, and a ventral vessel below the gut but above the nervous cord.
The dorsal vessel also communicates with the ventral vessel indirectly by the intestinal sinus, which gives off branches to both the longitudinal trunks, and by tegementary vessels and capillaries which supply the skin and the nephridia.
In the smaller and simpler forms the capillary networks are much reduced, but the dorsal and ventral vessels are usually present.
In this worm the ventral blood-vessel is so swollen as to occupy nearly the whole of the available coelom.
Setae always present and often very large, much varied in form and very numerous, borne by the dorsal and ventral parapodia (when present).
The prostomium bears often processes, both dorsal and ventral, which in the Sabellids are split into the circle of branchial plumes, which surround or nearly surround the mouth in those tube-dwelling Annelids.
Tomopteris is remarkable for the fact that the hammer-shaped prostomium has paired ventral processes each with a single seta.
In these forms the bundles of setae are either capilliform or uncinate, and the dorsal setae of the thorax are like the ventral setae of the abdomen.
Appendages of body re „ duced to branchiae, present only in four species, and - - to the ventral copulatory 32 appendages of Alma and Criodrilus.
Of body numerous and not A, B, C, anterior segments from the distinctive of species, being ventral surface; D, hinder end of body irregular and not fixed in of Urochaeta.
Several specially large contractile trunks in the anterior segments uniting the dorsal and ventral vessels.
The vascular system is simple with as a rule direct communication between dorsal and ventral vessels in each segment.
Vascular system complicated without regular connexion between dorsal and ventral vessels, except in anterior segments.
There are two chitinous jaws in the buccal cavity, a dorsal and a ventral, which are of specially complicated structure in Cirrodrilus.
The median lacuna no longer exists, but is represented by a dorsal and ventral sinus.
C antero-posterior direction, its ventral lobe usually concealing the mouth.
A ventral vessel occurs on the anterior side of the metasome and forms a loop extending down the entire length of the stalk, while a " heart " projects into the cavity of the pericardium, probably connected on the ventral side of the notochord with the ventral vessel, and on its dorsal side with the dorsal vessel.
At their opposite ends the dorsal and ventral vessels are probably connected with one another by means of a splanchnic sinus surrounding the stomach.
Op., Operculum, or ventral lip. ov., Ovary.
Beneath the epidermis is a longitudinal layer of muscle-fibres which are separated into four distinct groups by the dorsal, ventral and lateral areas; these are occupied by a continuation of the epidermic layer; in the lateral areas run two thin-walled tubes with clear contents, which unite in the anterior part of the body and open by a pore situated on the ventral surface usually about a quarter or a third of the body length from the anterior end.
These processes stretch across the body cavity to be inserted in the dorsal and ventral middle lines.
S, Opening of segmental tubes (placed by mistake on the dorsal instead of the ventral surface).
In some species of Rana and Staurois inhabiting mountainous districts in south-eastern Asia, the larvae are adapted for life in torrents, being provided with a circular adhesive disk on the ventral surface behind the mouth, by means of which they are able to anchor themselves to stones.
In other species, however, a peculiar type of polystely is met with, in which the original diarch stele gives rise to se-called dorsal and ventral stelar cords which at first lie on the surface of the primary stele, but eventually at a higher level separate from it and form distinct secondary steles resembling the primary one.
If we consider a leaf of the common fern we find that in its young condition it is closely rolled up, the upper or ventral surface being quite concealed.
It is homologous with the distal ends of the ceratohyals or ventral elements of the hyoidean or second visceral arch.
Sometimes the pad is reduced to a ventral semi-ring or meniscus; it retains its largest almost original shape and size in the second vertebra, the axis or epistropheus, where it forms a separately ossifying piece which connects, and coossifies with, the odontoid process (the centrum of the atlas) and the centrum of the second vertebra.
Sometimes the ventral portions of these pads form paired or un paired little ossifications, then generally described as intercentra; such are not uncommon on the tail.
Dorsal vertebrae frequently have a ventral outgrowth of the centrum; these hypapophyses may be simple vertical blades, I-shaped, or paired knobs; they serve for the attachment of the thoracic origin of the longus collianticus muscle, reaching their greatest development in Sphenisci and Colymbidae.
The ventral portion of the neck is formed by the strong crista inferior, on the median side of which is the deep fosses subtrochanterica by which air sacs enter the humerus.
The ventral inner margin of the preacetabular portion of the ilium is attached to the pre-sacral vertebrae, whilst the inner and dorsal margin of the postacetabular portion is attached to the primary sacral and the postsacral vertebrae.
The flexor digitorum sublimis muscle arises fleshy from the long elastic band which extends from the inner humeral condyle along the ventral surface of the ulna to the ulnar carpal bone, over which the tendon runs to insert itself on the radial anterior side of the first phalanx of the second digit.
The last nerve which contributes to the ischiadic plexus leaves the spinal column in most birds either between the two primary sacral vertebrae, or just below the hindmost of them, and sends a branch to the pubic portion which is composed of post-ischiadic nerves, partly imbedded in the kidneys, and innervates the ventral muscles between the tail and pubis, together with those of the cloaca and copulatory organs.
3.) The middle ear communicates with the mouth by the Eustachian tubes, which pass between the basisphenoid and basioccipital bones, and unite upon the ventral side of the sphenoid, a little behind its articulation with the pterygoids, where they open into the mouth cavity by a short membranous duct.
The whole ventral surface of the pericardium is exposed when the sternum is removed.
(I) The right and left carotids converge towards the middle and extend up the neck, imbedded in a furrow along the ventral surface of the cervical vertebrae.
Further, according to these muscles being inserted only upon the dorsal, or only upon the ventral, or on both ends of the semi-rings, we distinguish between an-, kat- and diacromyodi.
On the other hand, the diacromyodian type can have been developed only from a strong muscular basis which could split into a dorsal and a ventral mass; moreover, no Passeres are known to be intermediate between those that are diacromyodian and those that are not.
(2) Passeres diacromyodi, in which some of the syrinx muscles are attached to the dorsal, and some to the ventral ends, those ends being, so to say, equally treated.
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.
A ventral dilatation of the urodaeum, is absent in all birds.
The penis, and its much reduced vestige of the female, is developed from the ventral wall of the proctodaeum.
- Syrinx muscles entirely lateral or attached to the dorsal or ventral corners of the bronchial semi-rings.
Vv, Ventral vessel.