Anatomy of the orbital fasciae and the third eyelid in dogs.

The connective tissue structures commonly referred to as the periorbita, orbital septum, muscular fasciae, and vagina bulbi or collectively, as the orbital fasciae were dissected then illustrated and described. Two sheets (layers) of the periorbita (endorbita) were found in our dogs. The periorbita should be renamed endorbita because of its anatomic relations. The periorbita did not always fuse with the periosteum of frontal and sphenoid bones. Rather, the periorbita and the periosteum were often distinct and separate; only medioventrally did several fibrous bands unite the superficial sheet of the endorbita with the periosteum. Two layers of the endorbita fused with the periosteum of the margin of the bony orbit and with the orbital ligament. The muscular fasciae were divided into 3 layers. The superficial layer extended caudally from the orbital septum, was thick, and was pierced by arteries, veins, and nerves. The middle layer was attached to the sclerocorneal junction and, at the temporal canthus of the eye, was divided into superficial and deep sheets. The deep portion was attached to the lateral angle of the third eyelid, similar to a strong ligament. The deep layer of the muscular fasciae extended caudally from the sclerocorneal junction in intimate contact with recti and oblique muscles of the eyeball. The deep portion of the deep muscular fascia covered the deep surface of all recti muscles and separated them from the retractor bulbi muscle. Intermuscular septa were observed between middle and deep muscular fascia layers.(ABSTRACT TRUNCATED AT 250 WORDS)