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In most fossil nautiluses, the siphuncle runs more or less through the center of each chamber, but in ammonites and belemnites it usually runs along the ventral edge of the shell. In some fossil straight shelled nautiloids, cylindrical calcareous growths ("siphuncular deposits") around the siphuncle can be seen towards the apex of the shell.
The external or ventral region refers to sutures along the lower (outer) edge of the shell, where the left and right suture lines meet. The external (or ventral) saddle, when present, lies directly on the lower midline of the shell. As a result, it is often called the median saddle. On suture diagrams the median saddle is supplied with an arrow ...
The ventral (from Latin venter 'belly') surface refers to the front, or lower side, of an organism. [38] For example, in a fish, the pectoral fins are dorsal to the anal fin, but ventral to the dorsal fin. The terms are used in other contexts; for example dorsal and ventral gun turrets on a bomber aircraft.
In anatomy, a suture is a fairly rigid joint between two or more hard elements of an organism, with or without significant overlap of the elements. [ 1 ] Sutures are found in the skeletons or exoskeletons of a wide range of animals, in both invertebrates and vertebrates .
Human anatomy is the scientific study of the morphology of the adult human. It is subdivided into gross anatomy and microscopic anatomy . Gross anatomy (also called topographical anatomy, regional anatomy, or anthropotomy) is the study of anatomical structures that can be seen by unaided vision.
Anatomy is often described in planes, referring to two-dimensional sections of the body. A section is a two-dimensional surface of a three-dimensional structure that has been cut. A plane is an imaginary two-dimensional surface that passes through the body.
Brachiopods have two valves (shell sections), which cover the dorsal (top) and ventral (bottom) surface of the animal, unlike bivalve molluscs whose shells cover the lateral surfaces (sides). The valves are unequal in size and structure, with each having its own symmetrical form rather than the two being mirror images of each other.
The septa are attached to the inside wall of the shell, thus dividing the phragmocone into camerae. Where the septum meets the shell a suture line forms; in some ammonoids these lines became extremely complex and elaborate, providing strength without the necessity of added weight. Elaborate sutures allowed for thinner shells, and hence less ...