The petrous portion, which contains the organ of hearing, is between and somewhat behind the other two portions, at the lower edge of the temporal bone, wedged between the sphenoid and the occipital bones. On its outer surface is the _external auditory meatus_, and from below projects a long sharp spine called the _styloid process_, to which several minor muscles are attached. In the same angle between the petrous and squamous portions lies the bony Eustachian tube. The =sphenoid= or =wedge bone=, so called because in the process of development it serves as a wedge, lies at the base of the cranium, forming as it were the anterior part of the floor of the cavity containing the brain. It is a large, bat-shaped bone and articulates with all the cranial and many of the facial bones, binding them all together. It has a body, two large wings, and two lesser wings and, appears on the outside of the skull between the frontal and the temporal bones behind the zygomatic process. In the adult the body of the sphenoid is hollowed out into the sphenoid sinuses, in which pus sometimes forms. =The Ethmoid Bone.=--In front of and below the sphenoid and extending forward to the frontal bone is the ethmoid, the last of the cranial bones. It consists of a horizontal cribriform or sieve-like plate, from either side of which depend lateral masses of ethmoid cells. To the inner side of these masses are attached the thin curved _turbinated bones_, superior and middle, while between them is a vertical plate that forms the bony septum of the nose. Rising from the upper surface of the cribriform plate is another vertical plate, the _crista galli_, with the olfactory grooves on either side for the reception of the olfactory bulbs, filaments of the olfactory nerve passing down through the perforations of the cribriform plate to the nose. For the brain, which fills almost the entire cavity of the cranium, is supported by the sphenoid and ethmoid bones internally, as it is protected externally by the other cranial bones. =Ossification of Sutures.=--If premature ossification of all the sutures occurs, _idiocy_ results, while in _cephalocele_ there is a gap in the ossifying of the bones so that the membranes or brain protrude. In _rickets_ the forehead is high and square and the face bones poorly developed, so that the head looks larger than it really is. In _Paget’s disease_ the bones enlarge and soften. This affects the head but not the face and often the first thing noticed is that the hat is too small. _Craniotabes_ is thinning of the bone in places, the bone becoming like parchment and being easily bent. It is generally caused by pressure of the pillow or the nurse’s arm. =Bones of the Face.=--The facial bones serve to form the various features of the face, which after all are merely organs of special sense. Many delicate muscles control the facial expression which, consciously or unconsciously, reflects the character of their owner.