The nasal cavity opens craniad by the large =nares= (Fig. 39, _j_; Fig. 42, _r_), which are bounded by the premaxillary and nasal bones. In the natural condition this opening is divided by a median cartilage which is continuous with the lamina perpendicularis (Fig. 43, _n_) of the ethmoid, thus forming a partition which divides the nasal cavity into two separate halves. From the floor of the cranial part of the cavity rises a ridge formed of the nasal crests of the maxillaries and premaxillaries, and the cranial portion of the vomer. Farther caudad the vomer spreads out in a horizontal plane and separates from the floor of the cavity, so that the nasal cavity is thereby divided by a horizontal partition into dorsal and ventral portions. The ventral portion is small, forming the inferior meatus of the nose; it ends caudally at the =choanæ= (posterior nares, Fig. 41, _o_) which lead into the nasopharynx. That portion of the nasal cavity lying dorsad of the vomer is almost completely filled by the ethmoid and the conchæ nasales, superior and inferior. It is bounded caudally by the lamina cribrosa of the ethmoid (Fig. 42, _o_). The nasal cavity communicates with the cranial cavity by the foramina for the olfactory fibres in the lamina cribrosa; with the nasopharynx by the choanæ; with the exterior of the body by the nares; with the mouth-cavity by the foramina incisiva or anterior palatine foramina (Fig. 42, _s_); with the orbit by the sphenopalatine foramen and the nasolachrymal canal. It communicates directly also with the frontal sinuses (Fig. 43, _m_, _m′_), the sphenoidal sinuses (Fig. 43, _l_), and with the cells of the labyrinths of the ethmoid. JOINTS AND LIGAMENTS OF THE SKULL. =Sutures of the Skull.=--The bones of the skull join each other by means of immovable articulations known as sutures. These sutures are designated by combining the names of the bones between which they are situated: as, =sphenofrontal= suture (=sutura sphenofrontalis=), between the sphenoid and frontal; =nasomaxillary= suture (=sutura nasomaxillaris=), between the nasal and maxillary bones. When a suture joins the two corresponding bones of opposite sides the prefix =inter= is used, as the =intermaxillary= suture (=sutura intermaxillaris=) between the maxillaries. The sutures bounding the parietals have, however, received special names not derived in this manner. The suture caudad of the parietals, separating them from the occipital and interparietal, is known as the =lambdoidal= suture; that between the two parietals is the =sagittal= suture; that separating the parietals and squamous portions of the temporals is the =squamous= suture; that between the parietals and frontals is the =coronal= suture. The suture separating the two frontals also is known as the =frontal= suture, in place of interfrontal.