Part 48 (1/2)

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 a.s.sumes 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 gray matter, but the gray const.i.tutes 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 (_arbor vit_) 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-tori-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?

[Ill.u.s.tration: 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.

737. The MEDULLA OBLONGATA, or that portion of the spinal cord which is within the skull, consists of three pairs of bodies, (_corpus py-ram-i-dale_, _res-ti-forme_, and _ol-i-vare_,) united in a single bulb.

[Ill.u.s.tration: Fig. 123. The base of the skull and the openings through which the cranial nerves pa.s.s. 1, 1, The first pair of nerves. 2, 2, The cribriform plate of the ethmoid bone through which this nerve pa.s.ses. 3, 3, The second pair of nerves. 4, 4, The optic foramen in the sphenoid bone; through which pa.s.ses 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 pa.s.s 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, pa.s.ses 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, pa.s.ses 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 pa.s.s 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 pa.s.s from the brain through this opening. 20, The spinal cord. 21, The foramen spinalis, through which the spinal cord pa.s.ses. 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.

738. 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.

[Ill.u.s.tration: 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 vit 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.

739. 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-facto-ry_. 2d. The _Optic_. 3d. The _Mo-tores Oc-u-lorum_. 4th. The _Pa-theti-cus_.