A Treatise on Anatomy, Physiology, and Hygiene (Revised Edition) by Calvin Cutter (lightweight ebook reader txt) 📖
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728. What is the medium of communication from one organ to another? 729–754. Give the anatomy of the brain and cranial nerves. 729. Of what does the nervous system consist? What constitutes an exception to this?
329730. The CEREBRO-SPINAL CENTRE consists of two portions: The brain, and the spinal cord. For convenience of description, the nervous system may be divided into the Brain, Cranial Nerves, Spinal Cord, Spinal Nerves, and the Sympathetic Nerve.
731. The term BRAIN designates those parts of the nervous system, exclusive of the nerves themselves, which are contained within the cranium, or skull-bones; they are the Cer´e-brum, Cer-e-bel´lum, and Me-dul´la Ob-lon-ga´ta. These are invested and protected by the membranes of the brain, which are called the Du´ra Ma´ter, A-rach´noid, and Pi´a Ma´ter.
Fig. 120.
Fig. 120. 1, 1, The scalp turned down. 2, 2, 2, The cut edge of the bones of the skull. 3, The external strong membrane of the brain (dura mater,) suspended by a hook. 4, The left hemisphere of the brain, showing its convolutions.
730. Of what does the cerebro-spinal centre consist? How is the nervous system divided? 731. What does the term brain designate? Name them. How are they protected? Describe fig. 120.
330732. The CEREBRUM IS divided into two hemispheres, by a cleft, or fissure. Into this cleft dips a portion of the dura mater, called the falx cer´e-bri, from its resembling a sickle. The apparent design of this membrane is to relieve the one side from the pressure of the other, when the head is reclining to either side. Upon the superior surface of the cerebrum are seen undulating windings, called con-vo-lu´tions. Upon its inferior, or lower surface, each hemisphere admits of a division into three lobes—the anterior, middle, and posterior. (Fig. 122, 123)
Fig. 121
Fig. 121. A section of the skull-bones and cerebrum. 1, 1, The skull. 2, 2, the dura mater. 3, 3, The cineritious portion of the cerebrum. 4, 4, The medullary portion. The dark points indicate the position of divided blood-vessels. 5, 5, The lateral ventricles.
732. How is the cerebrum divided? What is the use of the falx cerebri? What is seen upon the superior surface of the brain? Its inferior?
331733. When the upper part of the hemispheres is removed horizontally with a sharp knife, a centre of white substance is brought to view. This is surrounded by a border of gray, which follows the depressions of the convolutions, and presents a zigzag outline. The divided surface will be seen studded with numerous small red points, which are produced by the escape of blood from the division of the minute arteries and veins. The gray border is called the cortical, or cineritious portion, while the white central portion is called the medullary. The two hemispheres are connected by a dense layer of transverse fibres, called cor´pus cal-lo´sum.
734. In the interior of the brain there are several cavities, two of which are of considerable size, and are called the lateral ventricles. They extend from the anterior to the posterior part of the brain, and wind their way into other parts of the cerebral organ.
Observation. In the disease called “dropsy of the brain,” (hydrocephalus internus,) the serum, or water, is usually deposited in these ventricles. This is effused from the many small blood-vessels of the membrane in these cavities.
735. The brain is of a pulpy character, quite soft in infancy and childhood; but it gradually becomes more and more consistent, and in middle age it assumes the form of determinate structure and arrangement. It is more abundantly supplied with blood than any organ of the system. No lymphatics have been detected, but it is to be presumed that they exist in this organ.
736. The CEREBELLUM is about seven times smaller than the cerebrum. Like that organ, it is composed of white and 332 gray matter, but the gray constitutes the larger portion. Its surface is formed of parallel plates separated by fissures. The white matter is so arranged, that when cut vertically, the appearance of the trunk and branches of a tree (ar´bor vi´tæ) is presented. It is situated under the posterior lobe of the cerebrum, from which it is separated by a process of the dura mater, called the ten-to´ri-um.
733. Describe the appearance of the brain when a horizontal section has been made. What is the gray border often called? What connects the hemispheres? 734. Describe the ventricles of the brain. In the disease called “dropsy of the brain,” where is the water deposited? 735. What is the character of the brain in childhood? In adults? 736. How does the cerebellum compare in size with the cerebrum?
Fig. 122.
Fig. 122. The under surface, or base, of the brain and origin of the cranial nerves. 1, 1, The anterior lobes of the cerebrum. 2, 2, The middle lobes. 3, 3, The posterior lobes, almost concealed by the cerebellum. 4, 4, The cerebellum. 7, 7, The longitudinal fissure that divides the brain into two hemispheres. 8, The first pair of nerves. 9, 9, The second pair of nerves. 10, The decussation, or crossing, of its fibres. 13, 13, The third pair of nerves. 14, The pons varolii. 15, 15, The fourth pair of nerves. 16, 16, The fifth pair of nerves. 17, The sixth pair of nerves. 18, 18, The seventh and eighth pair of nerves. 19, The medulla oblongata, with the crossing of some of its fibres exhibited. 20, The ninth pair of nerves. 21, The tenth pair of nerves, 22, The eleventh pair of nerves. 23, The twelfth pair of nerves.
Describe this portion of the brain. Explain fig. 122.
333737. The MEDULLA OBLONGATA, or that portion of the spinal cord which is within the skull, consists of three pairs of bodies, (cor´pus py-ram-i-da´le, res-ti-for´me, and ol-i-va´re,) united in a single bulb.
Fig. 123.
Fig. 123. The base of the skull and the openings through which the cranial nerves pass. 1, 1, The first pair of nerves. 2, 2, The cribriform plate of the ethmoid bone through which this nerve passes. 3, 3, The second pair of nerves. 4, 4, The optic foramen in the sphenoid bone; through which passes the second pair of nerves. 5, 5, The sphenoidal fissure. 6, 6, The third pair of nerves. 7, 7, The fifth pair of nerves. 8, 8, The ophthalmic branch of the fifth nerve. The third, the ophthalmic branch of the fifth and the sixth nerve pass from the brain through the sphenoidal fissure to the eye. 9, 9, The superior maxillary branch of the fifth nerve. 10, 10, The foramen rotundum, (round opening,) through which the nerve 9, 9, passes to the upper jaw. 11, 11, The inferior maxillary branch of the fifth pair. 12, 12, The foramen ovale, (oval opening,) through which the nerve 11, 11, passes to the lower jaw. 13, 13, The sixth pair of nerves. 14, 14, The seventh and eighth pair of nerves. 15, 15, The opening in the temporal bone, through which the seventh and eighth nerves pass to the face and ear. 16, 16, The ninth pair of nerves. 17, The tenth pair of nerves. 18, 18, The eleventh pair of nerves. 19, 19, The foramen lacerum (rough opening.) The ninth, tenth, and eleventh nerves pass from the brain through this opening. 20, The spinal cord. 21, The foramen spinalis, through which the spinal cord passes. 22, 22, The position of the anterior lobe of the brain. 23, 23, The middle lobe. 24, 24, The posterior lobe. 25, 25, A section of the skull-bones.
737. Describe the medulla oblongata. Explain fig. 123.
334738. The DURA MATER is a firm, fibrous membrane, which is exposed on the removal of a section of the skull-bones. This lines the interior of the skull and spinal column, and likewise sends processes inward, for the support and protection of the different parts of the brain. It also sends processes externally, which form the sheaths for the nerves, as they quit the skull and spinal column. The dura mater is supplied with arteries and nerves.
Fig. 124.
Fig. 124. A vertical section of the cerebrum, cerebellum, and medulla oblongata, showing the relation of the cranial nerves at their origin. 1, The cerebrum. 2, The cerebellum, with its arbor vitæ represented. 3, The medulla oblongata. 4, The spinal cord. 5, The corpus callosum. 6, The first pair of nerves. 7, The second pair. 8, The eye. 9, The third pair of nerves. 10, The fourth pair. 11, The fifth pair. 12, The sixth pair. 13, The seventh pair. 14, The eighth pair. 15, The ninth pair. 16, The tenth pair. 10, The eleventh pair. 18, The twelfth pair. 20, Spinal nerves. 21, The tentorium.
738. Describe the dura mater. What is its use? Explain fig. 124.
335739. The ARACHNOID, so called from its extreme tenuity, is the serous membrane of the brain and spinal cord, and is, like other serous membranes, a closed sac. It envelops these organs, and is reflected upon the inner surface of the dura mater, giving to that membrane its serous investment.
740. The PIA MATER is a vascular membrane, composed of innumerable vessels, held together by cellular membrane. It invests the whole surface of the brain, and dips into its convolutions. The pia mater is the nutrient membrane of the brain, and receives its blood from the carotid and vertebral arteries. Its nerves are minute branches of the sympathetic, which accompany the branches of the arteries.
741. The CRANIAL NERVES, that connect with the brain, are arranged in twelve pairs. They are called: 1st. The Ol-fact´o-ry. 2d. The Op´tic. 3d. The Mo-to´res Oc-u-lo´rum. 4th. The Pa-thet´i-cus. 5th. The Tri-fa´cial. 6th. The Ab-du-cen´tes. 7th. The Por´ti-o Du´ra. 8th. The Por´ti-o Mol´lis. 9th. The Glos´so-pha-ryn´gi-al. 10th. The Pneu-mo-gas´tric. 11th. The Spi´nal Ac´ces-so-ry. 12th. The Hy´po-glos´sal.
742. The OLFACTORY NERVE (first pair) passes from the cavity of the skull through many small openings in a plate of the eth´moid bone. (This plate is called crib´ri-form, from its resemblance to a sieve.) This nerve ramifies upon the membrane that lines the nasal passages. It is the softest nerve of the body. (Fig. 136.)
743. The OPTIC NERVE (second pair) passes from the interior of the cranium, through an opening in the base of the skull, (fo-ra´men op´ti-cum,) to the cavity for the eye. It pierces the coats of the eye, and expands in the retina.
744. The MOTORES OCULORUM (third pair) pass from the 336 brain, through an opening of the sphe´noid bone, (sphe-noid´al fis´sure,) to the muscles of the eye.
739. Describe the arachnoid membrane. 740. What is said respecting the pia mater? 741. How many pairs of cranial nerves? Name them. 742. Describe the olfactory nerve. 743. The optic nerve. 744. Describe the motores oculorum.
745. The PATHETICUS (fourth pair) passes from the brain, through the sphenoidal fissure, to the superior oblique muscle of the eye.
Fig. 125.
Fig. 125. The distribution of the third, fourth, and sixth pairs of nerves, to the muscles of the eye. 1, The ball of the eye and rectus externus muscle. 2, The upper jaw. 3, The third pair, distributed to all the muscles of the eye, except the superior oblique, and external rectus. 4, The fourth pair passes to the superior oblique muscle. 6, The sixth pair, is distributed to the external rectus muscle.
746. The TRIFACIAL NERVE (fifth pair) is analogous to the spinal nerves in its origin by two roots, from the anterior and posterior columns of the spinal cord. It
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