THE INTERIOR OF THE SKULL 189 



The medial wall (Fig. 192) is nearly vertical, and is formed from before back- 

 ward by the frontal process of the maxilla, the lacrimal, the lamina papyracea 

 of the ethmoid, and a small part of the body of the sphenoid in front of the optic 

 foramen. Sometimes the sphenoidal concha forms a small part of this wall (see 

 page 152). It exhibits three vertical sutures, viz., the lacrimomaxillary, lacrimo- 

 ethmoidal, and sphenoethmoidal. In front is seen the lacrimal groove, which lodges 

 the lacrimal sac, and behind the groove is the posterior lacrimal crest, from which 

 the lacrimal part of the Orbicularis oculi arises. At the junction of the medial 

 wall and the roof are the frontomaxillary, frontolacrimal, frontoethmoidal, and 

 sphenofrontal sutures. The point of junction of the anterior border of the lacrimal 

 with the frontal is named the dacryon. In the frontoethmoidal suture are the 

 anterior and posterior ethmoidal foramina, the former transmitting the nasociliary 

 nerve and anterior ethmoidal vessels, the latter the posterior ethmoidal nerve and 

 vessels. 



The lateral wall, directed medialward and forward, is formed by the orbital 

 process of the zygomatic and the orbital surface of the great wing of the sphenoid ; 

 these are united by the sphenozygomatic suture which terminates below at the 

 front end of the inferior orbital fissure. On the orbital process of the zygomatic 

 bone are the orbital tubercle (Whitnall) and the orifices of one or two canals which 

 transmit the branches of the zygomatic nerve. Between the roof and the lateral 

 wall, near the apex of the orbit, is the superior orbital fissure. Through this fissure 

 the oculomotor, the trochlear, the ophthalmic division of the trigeminal, and the 

 abducent nerves enter the orbital cavity, also some filaments from the cavernous 

 plexus of the sympathetic and the orbital branches of the middle meningeal artery. 

 Passing backward through the fissure are the ophthalmic vein and the recurrent 

 branch from the lacrimal artery to the dura mater. The lateral wall and the floor 

 are separated posteriorly by the inferior orbital fissure which transmits the maxillary 

 nerve and its zygomatic branch, the infraorbital vessels, and the ascending branches 

 from the sphenopalatine ganglion. 



The base of the orbit, quadrilateral in shape, is formed above by the supra- 

 crbital arch of the frontal bone, in which is the supraorbital notch or foramen for 

 the passage of the supraorbital vessels and nerve; below by the zygomatic bone and 

 maxilla, united by the zygomaticomaxillary suture; laterally by the zygomatic 

 bDne and the zygomatic process of the frontal joined by the zygomaticofrontal 

 suture; medially by the frontal bone and the frontal process of the maxilla united 

 by the frontomaxillary suture. 



The apex, situated at the back of the orbit, corresponds to the optic foramen 1 

 a short, cylindrical canal, which transmits the optic nerve and ophthalmic artery. 



It will thus be seen that there are nine openings communicating with each 

 orbit, viz., the optic foramen, superior and inferior orbital fissures, supraorbital 

 foramen, infraorbital canal, anterior and posterior ethmoidal foramina, zygomatic 

 foramen, and the canal for the nasolacrimal duct. 





THE INTERIOR OF THE SKULL. 



Inner Surface of the Skull-cap. The inner surface of the skull-cap is concave 

 and presents depressions for the convolutions of the cerebrum, together with 

 numerous furrows for the lodgement of branches of the meningeal vessels. Along 

 the middle line is a longitudinal groove, narrow in front, where it commences at 

 the frontal crest, but broader behind ; it lodges the superior sagittal sinus, and its 

 margins afford attachment to the falx cerebri. On either side of it are several 



1 Some anatomists describe the apex of the orbit as corresponding with the medial end of the superior orbital fissure. 

 It seems better, however, to adopt the statement in the text, since the ocular muscles take origin around the optic 



foramen, and diverge from it to the bulb of the eye. 





