ORBIT OF THE EYE. 121 



The diameter of the cavity passes obliquely outward from 

 the apex behind. As the figure is irregular, the side next the 

 nose does not partake of this general obliquity, but extends in a 

 straight direction from behind forwards. 



The orbit is somewhat contracted at its orifice, and enlarged 

 immediately within. The form of the orifice is rather oval, as 

 the transverse diameter is longer than the vertical. Seven bones 

 are concerned in the formation of this cavity ; the os frontis and 

 a portion of the lesser wing of the sphenoid bone above, the os 

 planum of the ethmoid, the os unguis, and the nasal process of 

 the upper maxillary bone, and the os palati below ; the osmalae, 

 and orbitar plate of the sphenoid bone, on the outside. 



On the upper surface is the depression for the lachrymal 

 gland ; and at the orifice is the notch or foramen for the supra- 

 orbitary vessels, See., which have already been mentioned. 



On the inner surface are two longitudinal sutures, which 

 connect the os planum and the os unguis to the os frontis above, 

 and the os maxillare below. In the upper suture are the two 

 internal orbitary foramina mentioned in the description of the 

 os frontis, the anterior of which transmits a fibre of the ophthal- 

 mic nerve, with an artery and vein ; the posterior transmits only 

 an artery and vein. There are also two smaller vertical sutures 

 on each side of the os unguis. On the anterior part of this 

 inner surface is the ridge of the os unguis, and the grooves for 

 accommodating the lachrymal sac, which passes into the canal 

 of the same immediately below. 



On the lower surface is the aforesaid canal, formed by the 

 nasal and orbitar process of the upper maxillary bone, and that 

 part of the os unguis which is anterior to the ridge. On the 

 posterior part of this surface is a groove which proceeds for- 

 wards, and penetrating into the bone, becomes a canal that 

 terminates in the infra-orbitar foramen ; this groove in the bone is 

 made a canal by the periosteum. The thin plate which forms this 



jaw. 12. The mental foramen. 13. The ramus of the lower jaw. 14. The 

 parietal bone. 15. The coronal suture. 16. The temporal bone. 17. The squa- 

 mous suture. 18. The upper part of the great ala of the sphenoid bone. 19. 

 The commencement of the temporal ridge. 20. The zygoma of the temporal 

 bone, assisting to form the zygomatic arch. 21. The mastoid process. 

 11 



