120 



ORBIT OF THE EYE, 



chin, and on the sides by the malar bones. If a per- 

 Fig. 28.* pendicular line be drawn down 



the face from the inner third of 

 the supra-orbital ridge to the inner 

 third of the body of the lower 

 jaw, it will intersect three fora- 

 mina, the supra-orbital, infra- 

 orbital, and mental, each giving 

 passage to one of the facial 

 branches of the fifth nerve, the 

 common seats of facial neu- 

 ralgia. 



The lateral region or side of 

 the head, comprises the tem- 

 poral and zygomatic fossae and 

 the mastoid portion of the tem- 

 poral bone. 



The inferior region or base of the skull, is very irregular 

 and presents an internal or cerebral and an external or basilar 

 surface. 



From the importance of the vessels and nerves which 

 traverse it, this region requires to be particularly studied. 



An acquaintance with the individual bones which compose the head is princi- 

 pally useful, as it leads to a perfect understanding of the whole structure, of 

 which each bone is but a small part. 



This structure comprises the cavities which contain the brain and the most 

 important organs of sense, as well as the foramina subservient to them, which 

 are of so much importance in the practice of medicine and surgery, and also 

 in physiology, that the following descriptions are subjoined. 



Orbit of the Eye. 



The figure of this cavity is that of a quadrangular pyramid 

 with its angles rounded ; so it resembles a cone, the bottom 

 being the apex and the orifice the base. 



* A front view of the skull. 1. The anterior portion of the frontal bone. 

 2. The nasal protuberance. 3. The supra-orbital ridge. 4. The optic foramen. 

 5. The sphenoidal fissure. 6. The spheno-maxillary fissure. 7. The lachrymal 

 fossa in the lachrymal bones, the commencement of the nasal duct. The figures 

 4, 5, 6, 7. are within the orbit. 8. The opening of the anterior nares, divided 

 into two parts bythevomer: the number is placed upon the latter. 9. The 

 infra-orbital foramen. 10. The malar bone. 11. The symphysis of the lower 



