we can move our jaw in the vertical direction, from side to side, and from before backwards. The teeth of man are likewise intermediate in structure between those of carnivorous and those of ruminant animals. Man, therefore, is omnivorous.

The "coronoid" process is a triangular, lofty plate of bone, which ascends beneath the zygomatic arch in order to increase the leverage of the temporal muscle which closes the jaw. Observe that the insertion of this muscle occupies only the inner surface and front border of the process; the outer surface of the process is occupied by the masseter. Respecting the "sigmoid notch" there is nothing to be said, except that it transmits the "masseteric " nerve and artery.

The walls of the lower jaw, particularly at the basilar part, are exceedingly compact and tough. In operations for removal of parts of the bone, it is necessary to use the saw freely, before the bone forceps can be of any service. The interior assumes the form of "diploe," and is traversed by the "inferior dental canal," which carries the vessels and nerves to the teeth. We have seen that the canal begins on the inner side of the ramus; if it be traced out by cutting away the inner wall, we shall find that it curves forwards, beneath the sockets of the teeth, and, towards the front, divides into two, of which one ends at the "foramen mentale," the other, much diminished in size, runs on through the diploe nearly to the symphysis, in order to convey vessels and nerves to the canine and incisor teeth.

The lower jaw has two centres of ossification, one for each lateral half. Their junction at the symphysis takes place about the close of the first year after birth. In the lower animals the symphysial suture remains throughout life.

SKULL AS A WHOLE.

The examination of the skull as a whole is easy and intelligible, provided the individual bones have been carefully studied.

Course of the First

sutures.

sutures.

of all we must learn the course of the This is of practical moment,-1, because it enables us to say with precision in what direction the head of the child is presenting during labour; 2, because in injuries of the skull we must not commit the error of mistaking a suture for a fracture;* 3, because it is desirable not to trephine in the course of the sutures.

The "coronal suture" (Plate XX. a) (fronto-parietal) connects the frontal with the parietal bones. It extends transversely across the top of the skull, from the great wing of the sphenoid on one side to the other. Concerning the construction of this suture we have to remember, that in the middle the frontal overlaps the parietal bones, whereas at the sides the parietals overlap the frontal a provision which manifestly tends to lock the bones together.

The "sagittal suture" (inter-parietal) connects the two parietal bones. It runs directly backwards, in the middle line, from the frontal to the occipital bone.

The "frontal suture" is formed by the union of the two halves of the frontal bone. It runs down the middle of the forehead, from the sagittal suture to the root of the nose. It always exists in infancy and childhood, but is generally obliterated in the adult. The "lambdoid suture" (Greek letter A) (occipito-parietal) unites the two parietals to the occipital bone.

The "occipito-mastoid suture,"† apparently a continuation of the

* Skilful as he was, Hippocrates once mistook a natural suture of the skull for a fracture, and was afterwards so ingenuous as to leave his mistake on record. On this, Celsus observes: "A suturis se deceptum esse Hippocrates memoriæ prodidit, more scilicet magnorum virorum, et fiduciam magnarum rerum habentium. Nam levia ingenia, quia nihil habent, nihil sibi detrahunt: magno ingenio, multaque nihilominùs habituro, convenit etiam simplex veri erroris confessio; præcipuèque in eo ministerio quod utilitatis causâ posteris traditur, ne qui decipiantur eâdem ratione, quâ quis antè deceptus est." (liber viii. cap. iv.)

This

†The old anatomists call this the "additamentum suturæ lambdoidalis." old name, as well as others mentioned in the text, e. g. "Coronal," "Sagittal," and "Lambdoid," are gradually falling into disuse, and giving place to more appropriate terms, derived from the bones connected, as, "inter-parietal," "frontoparietal," &c.

lambdoid, connects the occipital with the mastoid portion of the temporal bone.

The mastoid part of the temporal is connected to the posterior inferior angle of the parietal bone by the "masto-parietal suture." The squamous part of the temporal is connected to the parietal bone by the "squamous suture" (squamo-parietal); and to the great wing of the sphenoid by the "squamo-sphenoidal" suture. Concerning these connections, we must observe the great extent to which the squamous bone overlaps the parietal; an adaptation which mainly strengthens the arch of the skull at the sides, and prevents the lateral expansion of the buttresses.

Wormian bones.

In the mastoid suture more frequently than in any other, we meet with what are termed "Wormian bones," or "ossa triquetra." They are like little islands of bone developed from distinct centres, in the membrane which connects the cranial bones. They vary in number and size. In the museum of the College of Surgeons there is the hydrocephalic skull of an adult (from the collection of the late Mr. Liston), in which there are upwards of one hundred of these little bones.

Of the sutures which connect the bones of the cranium with the face, there is one which deserves notice, as being very comprehensive. It is called the "transverse frontal suture." It extends from the external angular process of the frontal bone, from one side to the other, across both orbits and the root of the nose (Plate XIII.). It connects the frontal with the malar, sphenoid, ethmoid, lachrymal, superior maxillary, and nasal bones. Other short sutures, such as the "spheno-malar," "spheno-parietal," "zygomatic," &c. speak for themselves.

We said that a knowledge of the sutures concerns midwifery. It enables us to say which way the head of the child is presenting. If we feel the meeting of the three sutures at the top of the occipital bone, we know the back of the head presents; if, on the other hand, we feel the "anterior fontanelle," or lozenge-shaped

So called after Olaus Wormius, a physician of Copenhagen, to whom the first description of these "complementary" bones has been assigned, but erroneously: they were known to Eustachius and Paracelsus.

space where four sutures meet, we know it is a forehead presentation.

THE SKULL-CAP.

Outer surface.

The skull-cap is composed of the expanded arches of three of the cranial vertebræ, and forms a beautiful oval dome for the protection of the brain. We all know the outward form of the head and that the greatest breadth of it is about the parietal protuberances. In a well formed European head, if we look at the dome of the skull-cap from above, (the beginning of the sagittal suture being in the centre of the perspective plane) we see scarcely anything but the smooth expanded vault of the cranium. But in the Negro and the Australian, the narrowness of the temples allows the zygomata to come into view, and in the most "prognathous" examples, the incisor teeth appear in front of the frontal sinuses. On the outer surface of the skull-cap there are a multitude of minute foramina, which transmit bloodvessels from the pericranium into the substance of the bone. Hence, if this membrane be torn off during life, the bone bleeds through minute pores. We observe on each side of the sagittal suture the "foramen parietale," which transmits a vein from the outside into the great longitudinal sinus: sometimes a small artery runs with it, and communicates with a branch of the middle meningeal. Along the side of the skull-cap we observe the curved line called the temporal ridge (Plate XIV.). It indicates the attachment of the temporal aponeurosis, and runs along the side of the frontal and parietal bones. The ridge circumscribes the "temporal fossa" which is formed by the frontal, parietal, temporal, sphenoid, and malar bones. The fossa gives origin to the temporal muscle, of which the tendinous rays, converging beneath the zygoma, are inserted into the coronoid process of the lower jaw. The size of the temporal fossa in all animals depends upon the size of the temporal muscle. Hence it is largest in the carnivora. In these animals the fossa occupies the whole side and upper part of the skull, and is increased in extent by bony ridges growing from