A typical cervical vertebra (from the third to the sixth inclusive) presents the following characteristics : - The body is smaller than in other regions of the column and is of oval shape with the long axis transverse. The lateral margins of the upper surface are raised into prominent lips, so that the surface is concave from side to side; it is also sloped downward in front. The inferior surface, on the contrary, projects downward in front and is rounded off at the sides to receive the corresponding lips of the adjacent vertebra. It is concave antero-posteriorly and convex in an opposite direction.
This is the u-shaped bone, so named from some resemblance to the Greek letter v. It is occasionally called the lingual bone, from its important relations with the tongue; it is situated at the base of the tongue, and may be felt between the chin and the thyroid cartilage. It consists of a body, two cornua, and two cornicula.
There are two bones named malar, (os malse, malare, jugale, zygomaticum.) Each is common to the face and orbit, forming the most prominent point of the side of the former, and the greater part of the outer border of the latter. Its form is quadrangular.
These bones of the coccyx (French: coccyx), when united together, which is usually the case in advanced life, are supposed to resemble a cuckoo's bill and are therefore called coccygeal. Most commonly there are four of them, sometimes but three; in a few instances five have been found. They diminish gradually in size from above downwards, which gives them, when taken together, a pyramidal form. As they are placed in a continuous line with the inferior third of the sacrum, they form a slightly concave surface anteriorly, a convex one posteriorly.
The sacrum, much the largest piece of the vertebral column, is placed, when the body is in the erect position, at the superior and posterior part of the pelvis, beneath the last lumbar vertebra, above the coccyx, and between the ossa innominata, between which it is inserted, in some measure like a keystone into an arch.
As in the intervertebral articulations, so in the union of the first portion of the sacrum with the last lumbar vertebra, there are two sets of joints -viz. (a) Class. -False Synchondrosis. (b) Class. -Diarthrosis. Subdivision. -Arihrodia (a) a synchondrosis, between the bodies and intervertebral disc; and (b) a pair of arthrodial joints, between the articular processes. The union is effected by the following ligaments, which are common to the vertebral column: -(i) anterior, and (ii) posterior longitudinal; (iii) lateral or short vertebral; (iv) capsular; (v) ligamenta flava; (vi) supraspinous and (vii) interspinous ligaments. Two special accessory ligaments on either side, viz., the sacro-lumbar and the ilio-lumbar, connect the pelvis with the fourth and fifth lumbar vertebrae.
The heart is formed by the blending in the median fine of two longitudinal endothelial tubes lying ventral to the fore-gut of the early embryo. Each tube is partially surrounded laterally by the splanchnic mesoderm which forms a septum between the right and left sides of the coelomic cavity. The blended endothelial tubes form the endocardium. The splanchnic mesoderm in relation to the endocardium becomes the myoepicardium, and the double layer connecting the heart dorsally and ventrally with the somatic mesoderm becomes the (temporary) dorsal and ventral mesocardia. The somatic mesoderm of the heart region becomes the pericardium.
The pericardium is a cone-shaped, fibro-serous sac which surrounds the heart and contains a small amount of fluid [liquor pericardii]. Its apex is above at the root of the great vessels, and its base below, adherent to the diaphragm. Its connection with the diaphragm is in part to the central tendon and in part to the muscle, especially on the left side. It consists of an outer fibrous layer and an inner serous layer. The virtual space between the serous pericardium and the epicardium is commonly called the pericardial cavity.
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