Orbital, Otic, and Occipital Regions
Orbital region.—The sclera (scl., [Fig. 14]) of the eye is cartilaginous. The optic foramen (opt. f.) is large and lies in connective tissue at the posterior limits of the orbit and sphenethmoid. At the posterior levels of the foramen the dorsolateral cranial roof cartilages, taeniatectí marginales (t. t. mar.) converge medially to form the posterior margin of the frontoparietal fontanelle and the tectum synoticum (tect. syn.) of the occipital region. At the posterior levels of the orbit the bursa angularis oris (b. ang. o., [Fig. 14]) is present adjacent to the maxillary.
Nerve foramina of otic and occipital regions.—The trochlear foramen lies within the bony margins of the optic foramen. The trochlear nerve is located posterodorsal to the optic tract, and separated from the latter by connective tissue. The oculomotor foramen (ocul. f.) lies in connective tissue posterior and ventral to the optic foramen ([Fig. 15]). Anteriorly, dorsally, and ventrally the foramen has a bony margin formed by the prootic (pro.); posteriorly, only a thin layer of connective tissue separates the oculomotor from the large prootic foramen (pro. f.). The latter is bordered by bone dorsally and by cartilage ventrally ([Fig. 16]). Posteriorly, bone separates the prootic foramen from the anterior acoustic foramen (ant. acus. f.), through which the ramus acusticus anterior and medius pass ([Fig. 17]). An extremely narrow bridge of cartilage separates the anterior acoustic foramen from the larger posterior acoustic foramen (post. acus. f.). The latter has a bony posterior margin and is widely separated from the bony jugular foramen (jug. f.) posteriorly ([Fig. 19]).
Figs. 14-15. Transverse sections through skull: 14) at level of optic foramen; 15) at level of oculomotor foramen. Abbreviations: angspl. angulosplenial; ant. r. pter., anterior ramus of pterygoid; ant. sq., anterior arm of squamosal; b. ang. o., bursa angularis oris; fpar., frontoparietal; fpar. fon., frontoparietal fontanelle; l. perp., lamina perpendicularis of frontoparietale; max., maxillary; Mc. c., Meckel's cartilage; ocul. f., oculomotor foramen; opt. f., optic foramen; pasph., parasphenoid; psdbas. proc., pseudobasal process; pter. proc., pterygoid process; scl., sclera; t. t. mar., taenia tecti marginalis; tymp. r., tympanic ring.
Pterygoid.—The anterior terminus of the pterygoid (pter., [Fig. 1]) appears at approximately the mid-length of the orbit as a small arcuate bone closely applied to the posterior maxillary process. Farther posteriorly the maxillary decreases in size, and the pterygoid and posterior maxillary process diverge medially from it. Posterior to this point of divergence, the posterior maxillary process is known as the pterygoid process (pter. proc.). The anterior terminus of the quadratojugal (qj.) lies medial to the maxillary at the level of the oculomotor foramen ([Fig. 14]).
Otic region.—The anterior end of the otic capsule (ot. cap.) is present at the anterior level of the oculomotor foramen. The anterior terminus of the pseudobasal process (psdbas. proc.) lies within the medial portion of the pterygoid at the posterior border of the oculomotor foramen ([Fig. 15]). The pseudobasal process abruptly increases in size. At the level of the prootic foramen ([Fig. 16]) the medial branch of the pterygoid diverges from the posterior ramus and is closely applied to the medial surface of the pseudobasal process. The otic process extends along the medial surface of the squamosal from the dorsolateral edge of the pseudobasal process, and then expands medially to meet the bony edge of the otic capsule and form the crista parotica. Posterior to the formation of the crista parotica, the ventral part of the otic process splits. The medial part forms the ventrolateral ledge of the otic capsule (vl. l. ot. c., [Fig. 20a-f]), whereas the lateral part moves ventrad in association with the ventral arm of the squamosal and fuses with the pterygoid process posteriorly.