Dorsal scale

“ The dorsal spines of the vertebrae are connected with a set of ossified ligaments binding the whole dorso-lumbar region into a rigid mass—another peculiarity in which the structure is strikingly like that of birds. ”

“ The cranial end of the centrum is convex and looks ventrocraniad when the centrum is horizontal. These peculiarities are more marked in the third vertebra than in the seventh. The spinous processes grow rapidly shorter as we pass craniad; the fifth, sixth, and seventh are directed dorsocraniad, the third and fourth dorsad.
Fig. 10.—Cervical Vertebræ, Side View.
a, spinous processes; b, cranial articular processes; c, caudal articular facet; d, intervertebral foramina; e, transverse process proper; f, processus costarius; g, wing of the atlas; h, dorsal arch of the atlas; i, atlantal foramen. ”

“ Each vertebra consists of a large ventral mass, the centrum, and an arch, the neural arch, roofing over the dorsal surface of the centrum; the arch is composed of several small plates of cartilage. The opening enclosed by each centrum and its neutral arch is the vertebral foramen; the joined vertebral foramina form the neural canal, which is occupied by the spinal cord.
Separate one of the vertebrae from the rest. The centrum is deeply concave at each end; such a centrum is termed amphicoelous. At the middle of the centrum the concavities meet and thus a canal is formed through it. ”

“ As the formation of bone predominates upon the side exposed to the light or the nervous, so does that of muscle upon the shady or vascular side. The abdominal side of the animal is the muscular, just as the dorsal side is the osseous. Upon the thorax, abdomen, on the members which belong to the anterior region of the body, and on the face, the muscular layer is by far the most predominant. ”

“ To obviate the pressure on the swollen and inflamed organ the position assumed is right lateral-dorsal, the body inclined to the right, the right thigh flexed on the pelvis, and the spinal column so curved as to relax the abdominal muscles of the right side. ”

“ The cervical vertebrae are smaller than those in any other region of the spine, and may be readily distinguished as they lie in the neck and extend from the base of the skull to the dorsal vertebrae, or the point of attachment of the first rib to the first dorsal. ”

“ A study of the spine will make clear the fact that if the cartilage between any two Dorsal vertebrae be thinned in front the bodies of the vertebrae will be closer together and the spinous processes more widely separated; the spinous process of the upper vertebra will be crowded against the one superior to it and that of the lower against the one inferior to it. ”

“ The neural arch forms the sides and roof of the neural canal, and at each end just above the centrum bears a pair of intervertebral notches for the passage of the spinal nerves, the posterior notches being considerably deeper than the anterior. The neural arch is drawn out into a series of processes. Arising [379] from the centre of the dorsal surface is a prominent median neural spine or spinous process, which projects upwards and slightly forwards ”

“ In the cranial region there is evidence of a double set of segments, which may be called somatic and splanchnic. The somatic segments, consisting of the outer skin and the body musculature, are doubly innervated as are those of the spinal cord by a series of ventral motor roots, the oculomotor or IIIrd nerve, the trochlear or IVth nerve, the abducens or VIth nerve, and the hypoglossal or XIIth nerve, and by a series of dorsal sensory roots, the sensory part of the trigeminal or Vth nerve. ”

“ The atlas vertebra transverse, nearly twice as broad as high; the central canal subtrigonal, narrow below. Skull nearly one-third the entire length of the body. Lachrymal bone wanting. The zygomatic process is formed of the malar bone. Vertebral column rough and rather spongy. Vertebræ 50: 7 cervical, 11 dorsal, 8 lumbar, 24 caudal. The atlas separate; the other 6 cervical united by their bodies and spines into one consolidated mass, and sometimes united to the first dorsal vertebra. The atlas subquadrangular, broader than long. The transverse process truncated. ”

“ The somatic muscles belonging to these dorsal segments are the eye-muscles, which are all dorso-ventral in position, and are not the same as the longitudinal somatic muscles, but belong to a distinct dorso-ventral segmental group, the only representative of which at present known in the mesosomatic region is the external rectus innervated by the VIth nerve. ”

“ No animal but man ever lies upon its back unless it is dead. Furthermore, the dorsal position puts tendons, nerves and muscles on a stretch, while the flexed lateral position puts these in a more or less relaxed position, which is most favorable to rest. ”

“ The latissimus dorsi has its origin by aponeurosis from the spinous processes of the six lower dorsal and all the lumbar and sacral vertebræ, from the crest of the ilium or hip bone, and from the three or four lower ribs, swings across the side, dwindling in size, and is inserted by a small tendon into the bicipital groove of the humerus or upper arm bone, thus covering in the part of the back not covered by the trapezius. It draws the arm down and back, raises the lower ribs, and draws the trunk forward, as in climbing. ”

“ Figure 20a is a section through the middle region of the head, cutting the hindbrain on one side and the forebrain on the other. The walls of the brain show rather more histological differentiation [319] than was seen in the preceding sections, though this cannot be shown under the low magnification used. The hindbrain (hb) , which is cut near its anterior border, exhibits the usual membranous dorsal and thick ventral walls. ”

“ Further, the relative weight of the cerebral hemispheres, as we ascend from the fish through the vertebrate sub-kingdom of animals, will be found to correspond to the variation of the face-line from a parallel with the dorsal surface.
To recapitulate: 1. The size and weight of the brain will be found to increase with the angle of the face to the axis of the body. 2. The expansion of the brain-case, with a proportionate diminution of the facial bones, is an invariable accompaniment of an increased facial angle throughout the vertebrate sub-kingdom of animals. ”

“ We must remember that on the dorsal surface of the foot in man we find but a single muscle—the dorsalis pedis. The remaining subcutaneous structures of this region consist of the tendons of the anterior muscles of the leg which occupy this dorsal aspect. ”

“ A large amount of ingenuity, it is true, has been spent in the endeavour to force the cranial nerves into a series of segmental nerves, which arise in the same way as the spinal by two roots, of which the ventral series ought to be efferent and the dorsal series afferent, but without success. ”

“ The outlet of the dorsal head-gland, usually called dorsal rib or dorsal tooth, projects prominently in the oral cavity. Deep in the buccal capsule are one pair of dorsal and one pair of ventral subniedian lancets. The caudal bursa of the male presents a short dorso- median lobe, which often appears as if it were divided into two lobes. The dorsal ray is divided to its base, its two branches are prominently divergent, and their tips are bipartite instead of tridigitate, as in A. duodenale. The common base of the dorsal and dorso-lateral rays is very short. ”

“ Two or three of the anterior dorsal vertebrae have very long slender spinous processes which in the living animal project beyond the general level of the skin forming distinct conical prominences, covered only by an exceedingly thin and naked integument. ”

“ The interior of the dorsal test shows no such apodemes as are found on the mesosternites, but, as I have shown in the discussion of the alimentary canal of Calymene and Ceraurus, there is an opening on either side of the axial lobe between the dorsal test and the abdominal sheath, and it is entirely probable that an extensor muscle passed through each of these. The abdominal sheath extends only along the posterior region of the glabella and the anterior part of the thorax, and probably served to protect the soft organs from the strain of the heavy muscles. ”

“ After emerging they break up into a large anterior division and a small posterior division, the posterior branches supplying the spine and the dorsal muscles and skin, the anterior the rest of the trunk and the limbs. The cervical plexus is formed by the anterior divisions of the first four cervical nerves, the brachial plexus by the last four cervical and the first dorsal or thoracic nerves, the lumbar plexus by the four upper lumbar, and the sacral plexus by the last lumbar and the four upper sacral nerves. ”

“ At the other end of the scale is man, whose spine is in a vertical line, and his face occupies a like plane. Between these two extremes are types which tend in various degrees, from the lower to the higher form, and just in proportion as the spinal axis approaches a vertical line from one side, the plane of the face approaches it from the other. ”

“ In Man, in consequence partly of the disposition of the articular surfaces of the vertebra, and largely of the elastic tension of some of the fibrous bands, or ligaments, which connect these vertebræ together, the spinal column, as a whole, has an elegant S-like curvature, being convex forwards in the neck, concave in the back, convex in the loins, or lumbar region, and concave again in the sacral region; an arrangement which gives much elasticity to the whole backbone, and diminishes the jar communicated to the spine, and through it to the head, by locomotion in the erect position. ”

“ If the vertebral column formed the axis of the human body, and supported the head and all the other parts in equilibrium, then might the upright position be a state of repose: but, as the human head does not articulate in the centre of gravity, as the chest, belly, and other parts press almost entirely forward with their whole weight, and as the vertebral column reposes upon an oblique base, a watchful activity is required to prevent the body from falling. Children who have large heads and prominent bellies can hardly walk at the end even of two years ”

“ Lateral curvature may arise in different ways, but in all cases it is due to the loss of the lateral balance of the body in the upright position, and is the result of an effort of nature to maintain the center of gravity of the body and support the head and shoulders in the position which requires the least expenditure of muscular effort. ”

“ The osseous system is developed uniformly with that of the nerves, and issues out of the vertebral column, as the nervous system does out of the spinal marrow; whilst the vertebral column forms at first but an isolating sheath around the latter, as an earthly substance most powerfully attracted by the nervous system, acting like the sun, and for the most part antagonistically upon the other parts of the body. In a somewhat similar manner, among falling bodies of different specific gravities, the heaviest will always lie undermost and nearest to the attracting centre of the earth. ”

“ No deformity of a child's body gives rise to so much alarm to parents, or is the subject of greater diversity of treatment among medical men, as lateral curvature of the spine, and this is due, I believe, to an imperfect acquaintance with its origin. Specialists are accustomed to treat lateral curvature, knock-knee, and flat-foot as distinct deformities, while in truth they are all links in the chain of one deformity. ”

“ The tissue of the neural arches does not any longer form a continuous sheet, but is divided into (1) a series of arches encircling the spinal cord, and (2) a basal portion resting on the cartilaginous sheath of the notochord. There are two arches to each muscle-plate, one continuous with the basal portion of the arch-tissue and forming the true arch, which springs opposite the centre of a vertebral body, and the second not so continuous, which forms what is usually known as the intercalated piece. Between every pair of true arches the two roots of a single spinal nerve pass out. ”

“ The weight of the body is reduced to the lowest possible limit consistent with its general size and the exercise of its functions. The limbs, for instance, take no part in the nutritive function, and are reduced in size to the weight of bone requisite for support and of muscle necessary to move the body. The head is just large enough to hold the brain, the organs of special sense, and the mouth with its organs. The neck is narrowed to a mere covering to the œsophagus, the vertebræ, and the muscles of head-support. ”

“ Some observations recently made in America show that even in adults of both sexes the two legs are rarely of equal length, and there must be, therefore, slight lateral curvature in all persons, and it is probable that these natural curves become exaggerated, as in the development of round shoulder the large antero-posterior curves of the spine are exaggerated. ”

“ In some cases, the curvature of the spine assumes an extreme type, the shoulders are rounded, and the head depressed, the face approximating the sternum, so that to see an object such as a picture on a wall, the patient must turn his back to it. ”

“ The morphological importance of the sections of the body-cavity in the head cannot be over-estimated, and the fact that the walls become developed into the muscular system of the head renders it almost certain that we must regard them as equivalent to the muscle-plates of the body, which originally contain, equally with those of the head, sections of the body-cavity. ”

“ SPINAL CORD, in anatomy, that part of the central nervous system in man which lies in the spinal canal formed by the vertebrae, and reaches from the foramen magnum to the lower margin of the first lumbar vertebra. It is about 18 in. long, and only occupies the upper two-thirds of the spinal canal. The cord is protected by the same three membranes which surround the brain. Outside is the dura mater, which differs from that of the brain in not forming a periosteum not to the bones, in sending no processes inward, and in having no blood sinuses enclosed within its walls. ”