Chap, iv.] THE ORBIT AND EYE. 4.1 



bleeding is checked without difficulty, the vessels 

 being capable of ready contraction. Large tumours 

 have been excised from the cortex of the brain, 

 without undue trouble from haemorrhage. 



CHAPTER IV. 



THE ORBIT AND EYE. 



THE orbit. The antero-posterior diameter of the 

 orbit is about If inches, its vertical diameter at the 

 base a little over \\ inches, audits horizontal diameter 

 at the base about \\ inches. The diameters of the 

 globe are as follows : transverse, 24 mm. ; antero- 

 posterior, 24-5 mm. ; vertical, 23 mm. (Brailey). The 

 eye-ball is therefore nearer to the upper and lower 

 margins of the orbit than it is to the sides, and the 

 greatest interval between the globe and the orbital 

 wall is on the outer side. The interior of the orbit is 

 most conveniently reached by incisions made to the 

 outer side of the globe, and, in, excision of the eye- 

 ball, the scissors are usually introduced on that side 

 when the optic nerve has to be divided. In excising 

 the left eye, however, it may be more convenient to 

 divide the optic nerve from the inner side. The 

 bones forming the floor, the roof, and the inner wall of 

 the orbital cavity, are very thin, especially in the last- 

 named situation. Thus, foreign bodies thrust into 

 the orbit have readily penetrated into the cranial 

 cavity, into the nose and ethrnoidal cells, and, when 

 directed from above, into the antrum. In sevei'al 

 instances, a sharp pointed substance, such as the end 

 of a stick or foil, has been thrust into the brain 

 through the orbit, and has left but little external 

 evidence of this serious lesion. Nelaton mentions a 



