The inferior region extends from the pos terior part of the nasal process to the occipital protubera.nce, and is circumscribed by a line, continuous with the extremities of the supe rior curved ridge of the occipital bone, and passing on the outside of the mastoid and in the direction of the zygomatic process of the temporal bone, to the crest which is on the temporal process of the great wing of the sphe noid. The facts to be here noticed are nu merous, and, to facilitate their enumeration, this region may be divided into three parts, one anterior to the pterygoid processes of the sphenoid bone, one posterior to the articu lating processes of the occipital bone, and a middle one between these two.
The anterior division contributes to form the nose and the orbits. For the first, there may be observed on the median line, the nasal lamella of the ethmoid bone, articulated, in front, to the nasal process of the frontal, and, behind, to the crest in front of the body of the sphenoid. On the same line, but below and behind this, is the azygos process, and inferior part of the body of the sphenoid, with the channels to form, with the vomer, the palatine canals. On either side of the nasal lamella is the slit for the ethmoidal nerve and vessels ; the cribriform plate and its foramina; and the space which assists to form the nares. More laterally, and still passing from before back wards, is the internal angular process of the frontal bone, to unite with the lachrymal ; the cellular mass of the ethinoid, with its turbi na.ted processes on one of its sides, and the orbitar plate on the other ; the junction of this mass to the body of the sphenoid ; the turbi noted process of the same bone, and, some times, the opening into its sinus; the articular surface for the palate bone ; and, lastly, the base of the pterygoid process exhibiting the anterior orifice of the Vidian canal.
Still more outwardly is the part which forms the orbit, concave, and broader before than behind. To the fore part there are, on the outer side, the lachrymal fossa; on the inner side the trochlear fossa, and, near to it, the orbitar orifice of the supra-orbitary foramen. Further back there is on the inner side a por tion of the transverse suture between the frontal and ethmoidal bones, containing the two internal orbital. foramina ; and, to the outer side, another portion of the same suture between the frontal and sphenoid. A third, shorter portion connects the two preceding, and unites the frontal to the small wing of the sphenoid. Behind this there are in succession the foramen opticum ; the foramen lacerum orbitale superius ; the foramen rotundum ; and, lastly, the sulcus temporalis leading from the last foramen, and being behind the orbitar process of the sphenoid bone.
The middle division offers in its centre the basilar process of the occipital bone, and the line of its junction with the sphenoid. On it are seen the indications of the attachment of the pharyngeal and anterior recti muscles. Its posterior edge forms a segment of a circle to assist in forming the foramen magnum.
On either side, and from before backwards, are the external and internal pterygoid pro cesses, with the fossa navicularis, fossa ptery goidea, and hiatus palatinus between the two processes; the posterior orifice of the Vidian canal; the foramen lacerum anterius ; the under surface of the petrous process of the temporal bone, with, on one side, the line of its junction with the basilar process, and, on the other, the line of its junction with the sphenoid bone, the Eustachian sulcus occu pying the latter; behind the foramen lacerum anterius is the rough surface for the origin of the levator palati and tensor tympani muscles; the inferior orifice of the carotid canal ; the opening of the aqueduct of the cochlea ; and, lastly, the foramen lacerum posterius. More outwardly, and pursuing the same direction, are the under surface of the great wing of tbe sphenoid bone; its line of union with the temporal ; .the processus articularis ; the fossa articularis; the Glasserian fissure ; the fossa parotidea ; and, lastly, the rough inferior bor der of the foramen auditorium externum. On the inner edge of this plane, and to the outer side of the sulcus Eustachianus, there are, successively, the foramen ovale ; the foramen spinale; the styloid process; the spinous pro cess, which is wedged into the Glasserian fis sure; the crest between the fossa parotidea and the foramen lacerum posterius ; the vagi nal process and the styloid process.
The posterior division exhibits, on the me dian line, the foramen inagnurn ; the longi tudinal spine bisecting the inferior curved ridge, and having, on each side, below that ridge, rough depressions for the attachment of the posterior recti muscles, and above that ridge, still stronger and larger marks of the attachment of the complexus ; and, lastly, the inferior aspect of the occipital protuberance. To the extreme outside and passing from behind forwards, there are the termination of the superior occipital ridge; the additamentum suturw lambdoidalis; the posterior part of the mastoid portion of the temporal bone dis playing the foramen mastoideum ; the sulcus occipitalis on one hand, the mammillary pro cess of the mastoid portion of the temporal bone on the other, and the sulcus digastricus between the two ; and, lastly, the foramen stylo-mastoideum at the bottom of the sulcus digastricus. Midway, and between the me dian and outer portions of this region, and still passing from behind forwards, there are, the superior occipital ridge, the inferior occipital ridge, and between them the marks of the attachment of the splenius capitis and trachelo mastoideus ; the oblique surface into which the obliquus capitis superior is inserted ; the posterior condyloid fossa, containing the pos terior condyloid foramen whenever it exists; the condyle itself; the anterior condyloid fossa and foramen; and, lastly, to the outside of the condyle, the processus lateralis.