Ventral scale

“ Although the ventral zone receives medullary fibers and itself produces nerve fibers, it sends, so far as yet observed, no fiber into the dorsal zone, but all the fibers which leave the ventral zone form nerve roots and leave the nervous system altogether. ”

“ This being a median section, the ventricles of the fore- (fb) , mid- (mb) , and hindbrain (hb) are seen as large cavities, while the cerebral hemispheres (ch) appear nearly solid, only a small portion of a lateral ventricle showing. The paraphysis (epi) is cut a little to one side of the middle and so does not show its connection with the brain. At the base of the brain the infundibulum (in) is seen as an elongated [331] cavity whose ventral wall is in close contact with a group of small, darkly staining alveoli (p) , the pituitary body. ”

“ Of the 246 specimens examined, 29 (11.8%; 11 females and 18 males) have an added [Pg 623] half-ventral immediately anterior to the anal plate. Of these specimens, 27 have the added half-ventral on the left side and two have it on the right. Five specimens have the last ventral divided similar to the normal division of the anal plate. One specimen has the last ventral incompletely divided transversely. Excluding the last ventral, seven specimens have divided ventrals (half-ventrals) . ”

“ The ventral and dorsal nerves are connected by a number of semicircular commissures, which originate from the ventral nerves and serve to supply the dorsal nerve, which is always being decreased by fibres departing from it. It is remarkable that these commissures are not placed symmetrically, and their position also is different in the two sexes; in the female there are thirty-one on the right side and only thirteen on the left side. ”

“ Insertion into the body of the sphenoid bone between the bulla and the middle line. The insertion extends craniad onto the basisphenoid.
Relations.—Ventral surface with the sternomastoid (Fig. 65, g) and the large lymphatic gland ventrad of the external [143] ear. Lateral surface with the scalenus (Fig. 72, h) and craniad with the levator scapulæ ventralis (Fig. 72, c-c′′) . Medial surface with the carotid artery, the trachea, œsophagus, and pharynx. Dorsal edge with the vertebræ, the longus colli (Fig. 72, g′) , and the rectus capitis anterior minor (Fig. 72, b) .
Action.—Lowers the snout. ”

“ Most all the nerve fibers produced within the brain enter the ventral territory, for in this territory we observe not only the fibers which it obviously must include—namely, those which are produced by the nerve cells of the ventral zone—but also the nerve fibers produced by the nerve cells of the dorsal zone. So far as at present known, the nerve cells of the dorsal zone all produce nerve fibers, but these fibers always pass into the ventral division of the nervous system. ”

“ The ventral plate is still rolled round the egg (fig. 7) , and the end of the tail and the procephalic lobes nearly meet dorsally, so that there is but a very slight development of the dorsal region. There are the same number of segments as before, and the chief differences in appearance between the present and the previous stage depend upon the fact (1) that the median ventral integument between the nerve ganglia has become wider, and at the same time thinner; (2) that the limbs have become much more developed; (3) that the stomodæum is definitely established ”

“ The whole sinus venosus has become part of the right atrium. It receives the three great venous trunks of the body, namely the vena cava superior dextra, the vena cava superior sinistra more dorsally, and the vena cava inferior more to the right and below; the opening of the last is guarded by two prominent valves in place of the mammalian valvula Eustachii. The right ventricle occupies the ventral portion of the heart. ”

“ Its cavity is known as the third ventricle. Just craniad of the [343] ’tween-brain, in the median line, is a deep fissure, showing that here in reality is the termination of the original tube, the further extension craniad being due to the pushing forward of the lateral outgrowths, or cerebral hemispheres, which extend in ventral view a considerable distance further craniad. The hemispheres lie also caudad, laterad, and dorsad of the midbrain and ’tween-brain, so that these parts are almost enveloped by the hemispheres. ”

“ Ven′trad (zool., anat.) , to or toward the belly, or ventral surface or aspect of the body; Ven′trally.—adj. Ven′tric.—n. Ven′tricle, a small cavity within an animal body, as in the heart or brain: (Shak.) the womb.—adjs. Ven′tricōse, Ven′tricous, swelling out in the middle: bellied; Ventric′ūlar. [L. ventralis—venter, the belly.]
Ventriculite, ven-trik′ū-līt, n. one of a genus of fossil sponges found in the cretaceous system, and often giving their shape to flint nodules. ”

“ At the sides, the brain is continued into two stout nerve-cords which encircle the oesophagus, and meeting, fuse together in the median ventral line to form the ventral nerve-cord (Fig. 211) . The latter is of the same diameter throughout, and shows no signs of segmentation; it is oval in section, and consists of small ganglion cells heaped up on the ventral surface, i.e. next the skin, and of numerous fibres situated dorsally. The cord gives off many nerves, which usually arise in pairs. These pass into the skin, and forming rings, run round the body, and give off finer nerves as they go. ”

“ The ventral portion is relatively more massive than in most animals; its anterior surface is concave and forms the main part of the articular surface for the occipital condyle of the skull. Its postero-dorsal surface articulates with the odontoid process of the axis. On its postero-lateral surfaces are the facets for articulation with the first ribs, which, unlike the other cervical ribs, have but one articular surface. Articulating dorsally with this ventral element of the atlas are the two rather heavy lateral elements which form the neural arch. ”

“ A verifying comment on this paragraph runs as follows:—“In the Hypotricha Infusoria, which creep over solid surfaces, there is a differentiation between ventral and dorsal surface and an approach to bilateral symmetry. The ventral surface is provided with movable cilia, the dorsal with immobile setæ.” ”

“ A portion of the nerve still continues to run along the side of the median ventral ridge, as far back as the point where the muscles of the hyoid segment pass round to the ventral side between the velum and the thyroid ”

“ Varices, longitudinal ribs in univalve shells.
Variety, is when one species differs some little degree from that of another.
Vaulted, like the roof of one’s mouth.
Venter, the belly, situated in the body of the shell; being the most prominent part when the aperture is turned to the observer.
Ventral, belonging to the belly.
Ventricose, inflated, swelled in the middle.
Vermiform, worm-shaped.
Vertex, in the Patella the top or most prominent part, situated in general nearly in the middle. In the genus Bulla it is used for the apex. ”

“ The body is thickly covered with nail-shaped spines about 10 μ long. Oral sucker 77 μ, to 85 μ in diameter. Ventral sucker characteristic and peculiar 0·12 to 0·14 mm. by 0·08 to 1 mm. It is a sac-like organ placed deeply in the body, but does not open as in other flukes on the ventral surface. Testes elliptical, not quite symmetrically placed at the hind end of the body. Vesicula seminalis retort-shaped, situated transversely, internal to the ventral sucker. ”

“ The ventral part generally remains cartilaginous as it does in man though sometimes it ossifies as in the armadillos. In the typical pronograde mammals the shape of the ribs differs from that of the higher Primates and man : they are so curved that the dorso-ventral diameter of the thorax is greater than the transverse while in the higher Primates the thorax is broader from side to side than it is dorso-ventrally. ”

“ A tube thus formed from the grooved ventral surface would carry with it to the new ventral surface the longitudinal venous sinuses, and thus form, in the way already suggested, the heart and ventral aorta. Posterior to the heart in the pronephric region, the same process would give rise to the sub-intestinal vein.
The evidence of comparative anatomy bears out most conclusively the suggestion that in the original vertebrate the gut was mainly a respiratory chamber. In man and all mammals the oral chamber opens into a small pharynx, followed by the œsophagus, stomach and small intestine. ”

“ The mesoderm that extends ventrad from the mesentery, on each side of the entoderm just described, consists of a thick layer of compactly arranged cells. The ventral end of the entodermal wall is fused with the wall of a small cavity, li, which may be traced several sections cephalad to this plane. This cavity is a part of the system of hollow liver trabeculae seen as a group of irregular masses of cells ventrad to the enteron at the opening of the anterior intestinal portal. The large blood vessel, bv, is the meatus venosus. ”

“ It is the tractus transversus peduncularis (Fig. 142, b) . Ventrad of the caudal corpus quadrigeminum is seen a triangular area of oblique fibres which corresponds in position to the human lemniscus.
The pedunculi cerebri (peduncles of the cerebrum) form the ventral part of the midbrain. They appear in a ventral view of the entire brain (Fig. 138) as two broad tracts of fibres (g) emerging from beneath the pons and diverging from one [352] another as they pass craniad, finally disappearing beneath the cerebral hemispheres. ”

“ They begin at their antero-ventral part near the genu of the corpus callosum and the anterior pillars of the fornix, and these are the parts which first appear in the lower mammals. The original anterior vesicle from which the hemispheres evaginate is composed, as already shown, of an anterior part or telencephalon and a posterior or thalamencephalon; the whole forming the third ventricle in the adult. Here the alar and basal laminae are both found, but the former is the more important; from it the optic thalami are derived, and more posteriorly the geniculate bodies. ”

“ When the stretching force is constant, the number of ventral segments is proportional to the rapidity of the hand’s vibration. To produce 2, 3, 4, 10 ventral segments requires twice, three times, four times, ten times the rapidity of vibration necessary to make the tube swing as a whole. When the vibration is very rapid the ventral segments appear like a series of shadowy spindles, separated from each other by dark motionless nodes. The experiment is a beautiful one, and it is easily performed. ”

“ Fig. 421. Section through the ventral part of the trunk of a young embryo of Scyllium at the level of the umbilical cord.
b. pectoral fin; ao. dorsal aorta; cav. cardinal vein; ua. vitelline artery; uv. vitelline vein united with subintestinal vein; al. duodenum; l. liver; sd. opening of segmental duct into the body-cavity; mp. muscle-plate; um. umbilical canal.
In all true Vertebrata the gland has a much more complicated structure. It arises as a ventral outgrowth of the duodenum (fig. 420, l) . ”

“ Probably the great development of the ventral elements of the pectoral and pelvic girdles in the plesiosaurs implies greatest development of the ventral muscles, used in the antero-posterior and downward movement of the paddles. ”

“ In addition to these the beginning of the ventral aorta is often thickened and expanded to form a bulbus arteriosus, which is non-contractile, and, strictly speaking, should rather be described with the arteries than with the heart. In relation to human embryology the smooth sinus venosus and reticulated auricle are interesting. Between the auricle and ventricle is the auriculo-ventricular valve, which primarily consists of two cusps, comparable to the two endocardial cushions of the human embryo, though in some forms they may be subdivided. ”

“ On the two anterior joints these spines are much shorter, appearing only as nodes. The ventral side is without spines, but is furnished with broad articulating faces. These characters indicate a great freedom of motion in the parts of the abdomen and account for the many positions in which this member is found.
Telson short and broad, flat and quadrangular on the ventral side; triangular and carinated on the dorsal side, and produced into a long, slender spine, having a length about equal to twice that of the posterior segment of the abdomen. ”

“ It also sends a branch to the ventral muscles and the integument of the neck, and three branches to various shoulder muscles.
VIII. The ventral branch of the eighth nerve (Figure 31) is the second largest nerve of the brachial plexus. It gives some twigs to the ventral muscles and then gives one or two nerves to the collo-thoraci-suprascapularis profundus and the serratus superficialis muscles. The rest of the nerve divides into an inferior and a superior branch which unite with the ninth nerve. ”

“ Ventral Cords.—The histology of the ventral cords and œsophageal commissures is very simple and uniform. They consist of a cord almost wholly formed of nerve-fibres, placed dorsally, and a ventral layer of ganglion cells (figs. 16 and 20) .
The fibrous portion of the cord has the usual structure, being formed mainly of longitudinal fibres, each probably being a bundle of fibres of various sizes, enveloped in a sponge-work of connective tissue. The larger bundles of fibres are placed near the inner borders of the cords. ”

“ It appears to me, (if the difficulties of comparing the Annelidan ventral cord with the spinal cord of Vertebrates are found to be insurmountable) , that this hypothesis would involve far fewer improbabilities than one which supposes the whole central nervous system of Vertebrates to be homologous with the super-œsophageal ganglia. The mode of formation of a nervous system presupposed in my hypothesis, well accords with what we know of the formation of the ventral cord in existing Annelids. ”