NERVOUS FUNCTION AND ITS ORGANS. CHAP. IX. vent. Practically we know from history that the greatest depravity and SECT. II. moral delinquency have been concealed under the most amiable appearance, whilst the best internal feeling, disposition and character may present a most forbidding countenance and demeanour. As "Man is practised in disguise, and cheats the most discerning eyes," it may be inferred that witnesses and prisoners will exhibit the most amiable appearance they can assume, and, therefore, it would be absurd to draw favourable conclusions from external appearances;(r) and, on the other hand, it is the duty of all to struggle against admitting the slightest prejudice, bias, or suspicion in respect of any assumed knowledge, either of cranioscopy or physiognomy, and to judge alone from the evidence and probabilities of each particular case. It has been remarked that the study of phrenology is too apt to encourage a conceitedness in superior powers of perception and sagacity, and, at least in courts of justice, would be a dangerous at tendant. Of particu. We will now proceed to examine the parts of the cranium and other lar parts of coverings of the brain in the order of the several successive layers of difthe head, ferent descriptions, namely, first, the hair, and skin, or scalp; secondly, the pericranium; thirdly, the plates of the bones of the skull, as the outer plate, the diploe, and the inner plate, called the vitreous; fourthly; the dura mater; fifthly, the arachnoid, or, more technically, the tunica arachnoidea; and, sixthly, the pia mater, immediately within which lie the brain and its vessels. especially the cranium and mem branes. The Hair, Skin, or Scalp, and Pericranium.-These may be termed the envelopes of the cranium. The hair and skin will be necessarily considered when we treat of the Integuments in general.(u) But with reference to some diseases and wounds of the head, these require particular local treatment, and have occupied the attention of the most eminent surgeons of the present time. (x) The Pericranium (from the Greek Tepi, about, and xpavov, the skull or helmet,) sometimes called the aponeurosis, covers the bones of the skull, and resembles and corresponds with and performs the office of the periosteum of other bones, being the external covering immediately over the external plate of the bones of the skull, and between the same and the scalp.(y) Blood vessels pass in the same, and into and through the external plate of the bone, and into the diploe between the two plates,(z) and this membrane is subject to the same changes as the periosteum in other parts of the body, and especially inflammation (a) simple and rheumatic.(b) (r) The guarded countenance is here alluded to; the instances of the sudden effect of shame or conscience will be considered towards the close of this chapter. (u) Post, chapter xi. (x) 1 Gibson, Surg. 122. Coop. Dict. tit. Head, as to the Scalp in particular. (y) Lizars, 31; G. Smith, 263; Coop. Dict. tit. Head; Copl. Dict. tit. Cranium; (z) 1 Bell, 36, 37; 1 Horn. Anat. 164. 2 12 a AND ITS ORGANS. 1. 1. Are parts of the Frontal CHAP. IX. bone forming the forehead. In SECT. II. general, the central division in NERVOUS the frontal bone does not exist FUNCTION like that in the particular skull here represented. The skull, however, usually has the appearance of an original division in the centre or along the mesial line, by a suture extending downwards to the root of the nose. At the lower and front part, two flat surfaces extend inwards, forming the roofs of the bony orbits. [a, a] 2. Is the left Parietal bone, forming the chief part of the lateral wall of the cranium or skull, and connected to the frontal bone by the coronal suture, and to its fellow along the mesial line, by the sagittal suture. 3. Is the Occipital bone or hind head, which is curved forwards below, forming a part of the base of the skull, in which it presents a large opening for the spinal marrow. It is connected to the two parietal bones by the lambdoidal suture. 4. The Temporal bone or temple, which contains the internal ear, divided into the tympanum and labyrinth. Its upper edge is thin and scaly; overlapping the edge of the parietal and sphenoid bones 6, forming the squamous suture. It has a long process [a] extending nearly horizontally forwards to meet the malar bone 8, which, with it, forms an arch or yoke, and underneath which the temporal muscle plays, and is the glenoid cavity for the head of the lower jaw and [d] the auditory canal. 5. The Ethmoid bone, of the spongy texture, entering largely into the structure of the nose, and its flattened sides bounding the orbit internally. 6. The Sphenoid bone, so called from its wedging in all the other bones of the cranium with all of which it is articulated, extends across and forms the middle part of the base of the skull, and is perforated by many holes for the transmission of a large number of the nerves of the brain, and gives attachment to some of the muscles of mastication. 7. The Superior Maxillary bone or upper jaw. It sends a process upwards [a] to form a part of the side of the nose. It forms the floor of the orbit [6,] and the half of the bony palate or roof of the mouth, along the mesial line of which it joins its. fellow. [c] Its infra orbitary foramen, for the second division of the fifth pair of nerves, distributed to the muscles of the face. Along its lower border eight teeth are inserted into the alveoli or sockets. The bone itself is hollow. 8. The Malar or Cheek bone, forming the projection of the cheek, and likewise entering into the composition of the orbit. It participates with the temporal bone in the formation of the bony arch under which the temporal muscle plays. [a] 9. The upper extremity of a small irregularly shaped bone called the Palate bone, which is placed between the sphenoid and superior maxillary, and enters into the composition of the orbit and of the bony palate. The soft palate and Uvula are attached to it. 10. The Os Unguis, so called from its resemblance to a finger nail. It forms a part of the orbit, and is grooved with the corresponding surface of the superior maxillary for the nasal duct, which conveys the tears from the eye downwards into the nose. 11. The two Nasal bones. These form the upper part of the projection of the nose; they are articulated with the frontal bone above, and the cartilage of the nose below. 12. The Inferior Maxillary bone, or Lower Jaw, (s) shaped somewhat like a horse (s) See description of lower jaw, ante, 69; and El. Blum. 313, 314, 317; 1 Horner, Anat. 152 to 155. CHAP. IX. shoe; a, a, is its base, d its angle. From the angle, a process of the bone mounts upSECT. II. wards, called the Rumus, which terminates in two processes, the posterior [b] is the NERVOUS rounded head, long in the transverse direction, and which rests in the socket [c] of the FUNCTION temporal bone. [4] The front process [c] affords insertion for the temporal muscle, and is called the coronoid process. It contains in the sockets or alveoli sixteen teeth ORGANS. in the adult. AND ITS General description and distribution of these bones in certain e. The mental foramen, from which emerges a branch of the inferior maxillary nerve, to be distributed to the muscles on the lower jaw. The bones of the Cranium, forming the parietes or walls for the Brain, are the frontal, two parietal, occipital, two temporal, Ethmoid, and Sphenoid. The bones entering into the composition of the Face are, the Frontal, two Nasal, two Superior Maxillary, two Malar, and lower Jaw. The orbit is formed by the Frontal, Lachrymal parts of the or Unguis, Ethmoid, Superior Maxillary, Palate, Sphenoid, and Malar. The thickness of the cranial bones varies in different subjects from that of the tenth part to that of one-third of an inch. The average is about one-fifth part of an inch The occipital bone is generally the thickest, and the temporal (the squamous portion of it) the thinnest, where it is covered by the temporal muscle. (t) entire head. Bones of The Bones of the Head and Skull.—It has been observed, that the the skull in anatomy of the skull is important, not in itself only, but that it provides general.(c) for a more accurate knowledge of the brain, explains in some degree the Of the organs of sense, instructs us in all those accidents of the head which are so often fatal, and so often require the boldest of all surgical operations. The marks which we take of the skull, record the entrance of arteries, the exit of veins and nerves, the places and uses of those muscles which move the jaws, the throat, the spine; indeed, in all the human body, there is not found so complicated and difficult a study as the anatomy of the head.(d) The bones of the cranium or skull cap in general are broad and flat, and bones of form the covering of the brain, and consist of two tables, thin plates, or the skull in layers, and an intermediate diploe, which answers to the cancelli of other general, bones: these tables are of the thickness of about one-tenth of an inch outer namely, each: the external is rather thicker, more spongy, and less easily broken; plate, di- the inner table is dense, thin, brittle, and more easily broken, and is someploe, and times fractured, although the external table remains entire; thence it is inner plate named tabula vitrea, or the glassy table.(f) These tables are parted from or vitrea. (e.) each other by the distance of a few lines (each the twelfth part of an inch,) and the intervening space is filled up with such diploe, cancelli or lattice work, which is a set of bony fibres covered with vessels, for nourishing the bone;(g) and by the dura mater (presently described,) adhering to the internal surface, and sending in arteries, which enter the cancelli by passing through the substance of the bone, and by the pericranium covering the external plate, and giving vessels from without, which also enter into the bone, the whole is connected into one system of vessels, and the aggregate is about the thickness of a quarter of an inch. The pericranium, dura mater, and skull, depend so entirely one upon the other, and are so truly parts of the same system, that an injury of the pericranium may affect the bone, separate the dura mater, and cause effusion upon the brain; whilst a separation of the dura mater may in like manner be followed by separation of the pericranium, which had been sound and (t) But see 3 Bost. 210, 211, ante, 245, where it is said, that in the same subject, the cranium is in all its parts of uniform thickness, and that thence, by its external surface, the means of acquiring an accurate knowledge of the convolutions that are subjoined to it are afforded. (c) Ante, 69; as to the bones of the head in general, see 1 Bell, 35 to 101; 2 Bell, 365; Coop. Dict. tit. Head; Copl. Dict. tit. Cranium; 1 Horner, Anat. 126 to 190. (d) 1 Bell, 35, 36. (e) See, in general, Coop. Dict. tit. Head; and Copl. Dict. tit. Cranium; 1 Horner, Anat. 156 to 178. (f) See, as to the bones of the Cranium, ante, 69. (g) As to the softened state of the diaploe in diseases, see Copl. Dict. tit. Craz nium. CHAP. IX. SECT. II. NERVOUS FUNCTION AND ITS anhurt; and every disease of the cancelli or substance of a bone is communicated both ways, inwards to the brain, so as to occasion very imminent danger, and outwards towards the integuments, and warn us that there is disorder within. The general thickness of the skull, and the natural order of the two tables, and an intermediate diploe, is very ORGANS. regular, in all the upper parts of the head. Idiotism is sometimes to be attributed to an original malformation of the cranium, sometimes in respect of acquired thickness, but more frequently in respect of shape; by each of which the internal cavity, and consequently the capacity of the brain, are unduly diminished.(h) Sutures.-All these external bones of the skull are joined together, or Sutures. as it is technically termed, articulated, by seams, which, from their indented or dove-tailed appearance, are named Sutures. Suture is a common term for the line of contact of the flat bones. It is a mode of union, admitting of no motion, and is somewhat varied according to the degree of pressure to be sustained.(2) This mode of junction was providentially designed to facilitate birth. (i) head. In the adult head, including the cranium and face, there are thirty Number of bones and thirty-two teeth. (j) These several bones have been enume- the bones rated in a preceding table,(k) and shown in situ in the antecedent plates;(1) of the those in page 54 give the frontal and posterior views of all the skeleton; that in page 259 is an exact representation of the bones of the head, disarticulated or separated for more convenient examination by students.(m) The following plate is a representation of the bones at the base of the skull. (h) 4 Good, 137; and see Copl. Dict tit. Cranium, and tit. Cretinism. (i) See a valuable note, 1 Bell, 40; and 1 Horn. Anat. 156 to 163; Dewees, Midwif. 41 to 44; and as to the course of the 1. Bony Cavity of the Nose. 3. The Two Incisor Teeth of 4. The Canine Tooth. 5. The Two Bicuspid Teeth. ble Teeth. 7. The End of the Bony Pa 8. The Zygomatic Process, 9. The posterior openings of 10. The Glenoid Cavity for the 11. The Carotid Canal, by 12. The Meatus Auditorius Ex- 13. The Foramen Jugulare, at growth of bone and of sutures, ante, 38, (j) 1 Bell, 39. CHAP. IX. 14. The Foramen Magnum, or Great Occipital Foramen, for the Passage of the SpiSECT. II. nal Cord. NERVOUS 15. The Mastoid Process of the Temporal Bone, for the Attachment of Muscles which move the Head on the Spine. FUNCTION AND ITS ORGANS. Os frontis. The two parietal bones. The two bones. 16. The Styloid Process, for the Attachment of some Muscles of the Os Hyoides, Tongue, and Pharynx. 17. The Occipital Bone: all its inferior Surface gives Attachment for Muscles, which maintain the Head in the upright Position. 18. The Condyles of the Occipital Bone, on which the Head revolves on the First Vertebra or Atlas. 19. Mesial Line, or Centre of the Skull. Os Frontis. (n)-This bone is situate in the front part of the skull and superior part of the face. It has been compared in shape to a clam shell; for it is of a semicircular shape, and hollowed like a shell. It is marked on the inside by a spine or prominent line, which divides the hollow of the bone into two equal parts, and give rise to a membranous partition called the falx, which perpendicularly divides and supports the hemispheres of the brain; and in some skulls this bone is divided in the centre by a distinct sutural line, and as represented in the plate, ante, 259. It is marked on the external surface by those high ridges on which the eyebrows are placed, and by two prominences, which are hollow caverns, named the sinus or cavities of the frontal bone. For a full description of every particular bone, the student is referred to Bell's Anatomy, (o) and, for the more modern view of the subject, to Dr. Quain's excellent work, [and 1 Horn. Anat. 128 to 143.] (p.) The Ossa Parietalia.-The two parietal bones form the roof of the skull; they are situated, as appears in the plates, ante, 54 and 259. They are convex externally, concave internally, and present two surfaces and four borders. The external surface rises towards its middle, where it presents the parietal prominences; below which is an oblique line, bounding a flat surface, which forms a part of the temporal fossa. The internal surface is marked by branching lines, corresponding with the course of the middle meningeal artery, by depressions for the convolutions of the brain; and along the superior border is a slight groove, corresponding with the longitudinal sinus. The superior border is straight, and articulated with its fellow by a series of dentations; the inferior concave, and levelled off at its margin, is overlapped by the squamous portion of the temporal bone. The anterior unites with the frontal bone, and the posterior with the occipital. The anterior inferior angle dips down to the sphenoid, and is marked internally by the meningeal artery; the posterior inferior angle articulates with the mastoid part of the temporal bone, and presents internally a part of the groove which lodges the lateral sinus.(q) The two parietal bones form much the greater share of the cranium; they are more exposed than any others, are the most frequently broken and the most easily trepanned. The square form of the bone produces four angles, and surgeons speak of the frontal, occipital, mastoidean, and temporal angles of the parietal bone. (r) The Ossa Temporalia.-On each side are two in the infant, but in temporal adults become ossified into one temporal bone. But it has been observed, that the temporal bones are divided into two only, by regarding the bony ring of the meatus auditorius as a distinct bone. These are situated at the lateral and inferior part of the skull. They close the cranium upon (n) See 1 Bell, 51; 1 Horn. Anat. 128 to 130. (o) 1 Bell, 51 to 59. (p) Quain's El. 106 to 108. |