Bony orbit

The case of the camera is the skull. The forehead and brow partially protect the eye that is enclosed in the bony orbit. To facilitate stereoscopic vision, the adult eyes are positioned such that the focus is able to converge to achieve a binocular view between 20 cm and infinity. The eyelids provide partial protection to sudden changes of light and also serve to compress and spread the tear film maintaining a clear optical surface. Fibrous tarsal plates provide the framework for the movable folds of modified skin (Figure 23.1a and Figure 23.1b). 

Starlings were assigned to two groups (n = 10/group). The birds in one group were lightly anesthetized with Equithesin, and placed in a head-holder. The olfactory nerves under the bony orbital walls were exposed. 

Medially, the bony orbit is confined by the ethmoid, lacrimal, sphenoid, and maxillary bones. The most anterior part of the medial wall of the orbit includes the nasolacrimal fossa, with the aperture of the nasolacrimal duct. 

Inferiorly, the orbital floor covers the top of the maxillary antrum and sinus. The orbital floor and the medial orbital wall are the weakest parts of the bony orbit. The orbital floor is shaped by the maxillary, zygomatic, and palatine bones. 

Anteriorly, the bony orbit ends in the orbital rim or entrance, which is the strongest part of the bony orbit. Covering or extending from the orbital entrance, the eyelid complex with its medial and lateral canthal tendons, the orbital septum, and the eyeball define the facial aspect of the orbit. The orbital septum is a thin, elastic membrane that separates the intra- and extra-orbital spaces and acts as an important barrier to disease (Fig. 12.1) (Hintschich and Rose 2005 Aviv and Casselman 2005). 

The subperiosteal space exists only when created surgically or filled in by a pathological process. It Hes between the bony orbital walls and the periorbita. The periorbita is loosely attached to all bones of the orbit and to the orbital septum and consists of multiple cormective tissue septa that separate the contents of the orbit from its bony confines. 

Fig. 5. Undersurface of the brain of a vitamin A-deficient puppy (litter mate). Note the tortuosity of optic nerves in the orbit, also compression deformities of cerebrum and cerebellum. The tortuous optic tract is evidence of failure of dimensional increase of the long bony orbit in a region which excludes deformation by pressure of bone.

The brain resides within the cranial cavity. The bony roof and sides of the cranial vault make up the calvaria, which is composed of frontal, temporal and parietal bones and a small portion of the occipital bone. The floor of the cranial vault is divided into three depressions or fossae the anterior fossa extends from the region superior to the orbits and nasal cavity caudaUy as far as the posterior margin of the lesser wing of the sphenoid the middle fossa occupies the region between the lesser wing of the sphenoid and the anterior border of the petrous portion of the temporal bone and the posterior fossa, is underlain by the remainder of the temporal bones and the occipital bone. 

The orbit is defined as the anatomic space in the skull that contains the eyeball and its accessory organs. At the orbital apex, many nerves and blood vessels pass from the orbit into the cranial cavity and vice versa. The orbit is pyramidal in shape, with four bony walls narrowing posteriorly toward the apex. 

The bony confines of the orbit include various foramina and fissures that accommodate different neurovascular structures, which are essential for normal ocular function (Table 12.2). 

The supraorbital neurovascular bundle passes through a bony canal or notch in the superior orbital rim and contains the frontal and lacrimal branches of the ophthalmic division of the trigeminal nerve (VI) (Aviv and Casselman 2005 TTintschich and Rose 2005). 

Fig. 12.2a-d. Fracture of the left orbital floor with associated fracture of the bony canal of the infraorbital nerve [arrows in axial (a), coronal (b), and sagittal (d) reformations] and fractures of the orbital floor (arrowheads in d) and the anterior, lateral, and posterior walls of the maxillary sinus (arrowheads... 

Fig. 12.4a-f. Orbital metastasis of prostate cancer affects major wing of sphenoid bone and extraconal compartment of orbit, with bony spiculae extending into the intra-oibital soft tissue mass (arrows). Metastasis causes proptosis of left eyeball (axial MDCT images, a and b), compression of optic nerve in... 

Traumatic lesions of neural structures within or surrounding the orbit seldom occur without associated bony or soft tissue injury to the orbit. They are most frequently associated with complex trauma to the face or the frontal neurocranium (Mueller-Forell and PiTZ 2004). MDCT and MRI are particularly useful to demonstrate the acute and chronic features of complex facial and neurocranial injury, and to visualize affection of the optic nerve canal (Linnau et al. 2003). 

Several grading systems of JAF have been presented but the Fisch classification [] is the most extensively used one. Fisch classifies JAF into four types. Fisch type 1 is when the tumor is limited to the nasopharynx and nasal cavity without bony erosion. Fisch type 2 defines a JAF that invades the pterygomaxil-lary fossa and the maxillary, ethmoid and parasellar region but remains lateral to the cavernous sinus. Type 3 is defined as JAF tumors that invade the infratemporal fossa, orbit and parasellar region but remain lateral to the cavernous sinus. Finally, the type 4 tumors are those that show massive invasion of the cavernous sinus, the optic chiasmal region, or the pituitary fossa. 

Hg. 11.24 Idemilicaiioa of ihesymnciries of ligand group orbitals and metal orbitals capable of pardcipatBc Birr bonis (represented as vectors) in an octahedral ML complex. The charactets and inedudble compoacius of the reducible representation. T., were detiwed by applkation of the same methods used for the o>only system (Fig, 11,18),... 

Figure 18.1 Dialipina salgueiroensis, head (CNM SI 125) Emsian, Anderson River. Northwest Territories, Canada. (A) Drawing (B) photo. dClei=dorsal cleithrum Gu=gular o.p =orbital process of maxilla PCIei=postcleithrum pe=pectoral fin pl.che=bony plates of the cheek region pl.lj=plates of the lower jaw sc=scale t =tooth plate of dentary t =tooth plate of maxilla tp =tooth plate of premaxilla vClei=ventral cleithrum. Scale equals I cm.

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