The Cerebrum, Cere bellum, and Oblongata. Medulla III. OF SENSIBLE PARTS. To point out what parts were fenfible, we have the following experiments. Upon touching the BRAIN* with a knife, or in whatever way Baron de HALLER did it, or upon applying any cauftic body, the animal was seized with violent convulfions, and contorted his body on the one fide or the other in the form of a bow, expreffing by its screams violent anguish. Having thruft a probe, fays Dr. J. JOHNSON, into The Spinal the SPINAL MARROW †, all the muscles of the limbs were violently convulfed.-The muf Marrow. The BRAIN is divided into two portions; that fituated in the upper part of the fkull, is called CEREB UM, and that in the hind part, under the former, CEREBELLUM. On the external furface of the brain we fee several inequalities, or windings, like the circumvolutions of the intestines, and the CEREBRUM divides into two hemispheres while the CEREBELLUM fends out an oblong projection, which paffes through the large hole of the occiput, called MEDULLA OBLONGATA. The MEDULLA SPINALIS, or fpinal marrow, is a continuation of the medulla oblongata. cles cles of the back were fo convulfed, that the animal was bent backwards as in opisthotonos of the lock-jaw. The intercostal muscles were all contracted, and their natural action, that of drawing all the ribs nearer each other and upwards, was rendered a matter of ocular demonstration. The diaphragm was also ftrongly contracted. The NERVES *, which derive their fource from The Nerves. the brain, are themselves extremely fenfible. It is impoffible to represent to one's self, without having seen it, the vast pain and disquietude which an animal is thrown into upon touching, irritating, or even tying a nerve. The SKIN †, as being abundantly supplied with The Skin nerves, is found to be extremely fenfible, for in whatever manner you irritate it, the animal makes a noise, struggles, and gives all the indications of pain that it is capable of. The * The nerves have been before described page xxvii. The SKIN is divided by anatomifts into two distinct coverings. The outer is called CUTICULA, or fcarf-fkin; the inner CUTIS VERA, or true skin. Between these is interpofed a flimy mucus, called RETE MUCORUM; The Membranes of the Stomach, Inteftines, Bladder, and Ureters. The INTERNAL MEMBRANES of the STOMACH, INTESTINES †, BLADDER‡, and URETERS, being of nearly the fame nature with the fkin §, does in confequence enjoy the fame fenfibility. MUCORUM; which is yellowish, brown, or black, as is the complexion. * This part has been described page xx. + Vide page xxi. The BLADDER is situated in the lower part of the belly, immediate ly behind the union of the pudendal bones, and above the rectum, or ftraight gut. It is the refervoir of the urine or aqueous part of the blood (a more particular account of the urine will be given when we come to Diabetes) fecreted by the kidneys and fent from thence by its ducts, or URETERS; its external paffage is called URETHRA, the neck of which, or more properly fpeaking the bladder, is fecured by a circular muscle called SPINCTER URINE, the fibres of which close this opening, except under the great irritationo f diftention, or from the commands of the will. The coats, or tunics, of the bladder are the fame as those of the inteftines, ftomach, and ofophagus, viz. an internal membranous, fenfible, and fecreting mucus, a middle muscular, and an external also membranous, but infenfible. The URETERS are tubes, about the fize of goofe-quills, and about a foot long; they arise from the kidnies, and enter the bladder near its neck, running for the space of an inch obliquely between its coats, they form to themselves as it were valves, fo that upon the contraction of the bladder, the urine is darted along the URETHRA, which is its proper paffage. Thefe feveral parts differ anatomically from the skin in this. They have no cuticle, nor rete mucofum, though they fecrete a fluid analogous to this. They differ from the skin alfo in having mufcular fibres immediately under them. The MUSCULAR FLESH is fenfible of pain, The Mufcles. which is dependant entirely on the nerves. For if you tie the nerve going to any part, that part becomes immediately paralytic below the ligature and infenfible. Its vital functions however remain. A blifter applied to the part below the incifed nerve inflames and draws up the outer fkin, though it does not create pain; ulcers are healed, and fuppurate, and the limb feems to have loft nothing but the power of motion. The Mammæ, or BREASTS*, as being covered The Breaft. with a good deal of fkin, and furnished with many nerves, has also a proportionable degree of fenfibility. Each BREAST is a CONGLOMERATE GLAND, or an affemblage of glands to feparate milk, with their EXCRETORY DUCTS, which are capable of much diftention, tending towards the nipple, and as they approach, unite, fo as to make but a few ducts at their exit. IV. OF IV, OF INSENSIBLE PARTS. In order to difcover what parts were infenfible, Baron de HALLER made the following experi ments. The Dura Mater. The DURA MATER * is a kind of periosteum, every where applied to the internal furface of the cranium, connected to it by veffels, and has arteries tranfmitted through it to the skull, in the fame manner as they are transmitted through the periosteum to the other bones of the body. It is composed, like all the other membranes of the body, of cellular fubstance, and like them is perfectly infenfible, so that it may be burnt with vitriol, cut with a knife, or tore with a pair of pincers, without the animal, the * The DURA MATER is a very compact strong membrane lining the infide of the skull, firmly adhering at its bafis, and but lightly at the upper part, except at the futures. It extends itself across the skull, fo as to divide the cerebrum into two hemifpheres. This part of the membrane is called the FALX, and prevents in great measure the concussion of this part. It again projects laterally, and sustains the posterior part of the cerebrum, which hinders it from compreffing the cerebellum. object |