730 CRANIUM. 



The orbitar portion by its upper surface Behind the external angular process, be- 



supports the anterior lobes of the brain, and tween the temporal fossa on the one hand and 



its under surface forms the root of the orbits, the orbitar process on the other, there is a 



It is divided into two processes by a longitu- triangular rough surface which is implanted on 



dinal notch, which corresponds to the roof of a similarly-disposed surface of the great wing 



the nose. of the sphenoid bone. The posterior margin 



The orbitar process of either side is convex of this surface is in apposition with the edge 

 in both directions on its upper surface, and of the thin extremity of the small wing of the 

 the mammillary eminences and d'igital im- sphenoid, to which also is articulated the re- 

 pressions formed by the intergyral spaces and maining portion of the posterior border of the 

 convolutions of the brain are of a decided orbitar process ; but with this difference, that, 

 character. On its under surface it is concave while in the former instance the edges are plain 

 .and triangular, the base being directed for- and simply applied to each other, in the latter 

 wards; at its anterior and outer part there is a the margins are denticulated, the sphenoid 

 J'ossa (fossa lachrymalis) for the lachrymal overlapping the frontal so as to render the 

 gland, 'and which is overhung by the external roof of the orbit secure. 



orbitar process ; at its anterior and inner part, Thus the frontal bone articulates by the pos- 



near to the internal orbitar process, and be- terior borders of its two portions, with the 



tween it and the foramen supra-orbitarium, parietal and sphenoid ; by the inner edges of 



there is a small pit (fossa trochlearis) to which its orbitar processes, with the ethmoid ; by its 



is fixed the cartilaginous pulley in which plays nasal process, with the nasal ; by its internal 



the tendon of the superior oblique muscle of angular process, with the lachrymal ; by the 



the eye; at the middle of its inner edge there surface between the nasal and internal angular 



is a notch t which, applied to a similar notch of processes, with the superior maxillary ; and by 



the ethmoid bone, constitutes the foramen its external angular process, with the malar 



orbitarium internum anticum, through which bones. 



pass the ethmoidal twig of the ophthalmic This bone in the fcetus, and for nearly two 



branch of the fifth pair of nerves, and the an- years after birth, consists of two pieces, the 



terior ethmoidal branch of the ophthalmic first deposit in each being at the prominence 



artery; and a little behind this there is another already indicated. From this point the ossific 



notch, which by a like contrivance forms a hole matter radiates, and approaching that from the 



(the foramen orbitarium internum posticum) opposite side, the two combine so as to form 



for the passage of the posterior ethmoidal on the median line a suture which is speedily 



branch of the ophthalmic artery and corres- effaced. Nevertheless it occasionally happens 



ponding vein. that complete union does not take place, and 



The notch which is between the orbitar pro- then the suture persists through life. 

 cesses is the hiatus ethmoidalis (incisura The ethmoid bone (yQposiSw, *j6/xo?, cribrum, 

 et/imoidulis), and in the cranium it is filled up osethmoideum; Germ.Ethmoidal-knochen)com- 

 by the cribriform plate of the ethmoid bone, pletes that portion of the base of the cranium, 

 Its longitudinal is twice the length of its trans- anterior to the sphenoid, which is not supplied 

 verse diameter; anteriorly, it is bounded by by the frontal. It is however devoted less to 

 the notch which, in part, forms the foramen the skull than to the face, with many of the 

 coecum and the posterior surface of the nasal bones of which it is connected; and it con- 

 process ; posteriorly, it is open ; and its sides tributes greatly to form the nostrils and their 

 are bounded by the commutual edges of the septum, as well as both of the orbits, 

 orbitar processes, the tables of which are sepa- As an element of the cranium it is very 

 rated in such a manner as to communicate with simple, being merely a plate connecting the 

 the ethmoidal cells and close them at the two orbitar processes of the frontal bone, and 

 upper part, and at the anterior part of the having on its median line a ridge, which joins 

 notch to communicate also with the frontal the frontal spine before, to the body of the 

 sinuses. sphenoid bone behind. This plate is the cri- 



The frontal sinus is formed by the separation brifonn plate or process; it is notched poste- 



of the two tables of which the bone is com- riorly where it receives the ethmoidal process 



posed, and by the absorption of the diploe ; of the sphenoid bone, the apex of which pro- 



they are usually separated by a septum, and cess is applied to the posterior extremity of the 



they communicate on -each side with the mid- central ridge. Advancing forwards, this ridge 



die meatus of the nose in the manner indi- quickly springs upwards as a pyramidal pro- 



cated above. cess (the crista galli, or processus cristatus), 



The posterior and upper border of the bone to which the falx cerebri is attached ; its pos- 



as far down as the posterior extremity of the terior edge is long and oblique, its anterior is 



inferior margin of the fossa temporalis, is arti- shorter, more vertical, and it terminates in- 



culated to the parietal bones ; and it will be feriorly in two slightly divergent plates, so as 



remarked that rather more than the middle to form by their articulation with the frontal 



third of it advances upon and secures those bone the foramen caecum. On each side of the 



bones at the expense of their outer table, while crista galli, more especially towards the fore- 



the inferior portions of it are in their turn part, the cribriform plate is channelled for the 



grasped by each parietal bone respectively, reception of the olfactory nerves, and each 



the outer table of the latter advancing, at this channel is perforated by numerous foramina 



part, upon the inner table of the former. for the transmission of the ramifications 



