248 Mammalia, 



The position of the parts in the Orbital Cavity may be 

 shortly reviewed as follows : The Supra-orbital and Lachry- 

 mal nerves lie close to the outer wall of the cavity ; and the 

 small Fourth nerve near the inner wall : all entering the Orbi- 

 tal cavity above the muscles. The Superior Oblique muscle is 

 recognised by the Fourth nerve entering it : the Levator 

 Palpebrse and Superior Rectus are crossed by the Fourth 

 nerve : the External Rectus is seen between the Supra-orbital 

 and the Lachrymal nerves. 



A small nerve, the Temporo-malar, or orbital branch of the 

 Superior Maxillary trunk, lies in loose fat, along the outer 

 angle of the floor of the orbit, and should be traced before 

 further dissection is made in that part, as it is soft and easily 

 broken : it is distributed to the eyelids and to the integu- 

 ment. 



Dissection of Spheno-Palatine Ganglion. The Perios- 

 teum, or Orbital Membrane, should now be dissected away 

 from the subjacent fat, and, together with the contents of the 

 orbit, turned towards the top of the skull ; and the fat removed. 



By this means the cancellous bony structure that projects 

 backwards along the base of the orbit in the direction of the 

 optic nerve will be disclosed ; and, immediately beneath it, 

 the Superior Maxillary division of the Fifth nerve : this stout 

 bundle of nerves should be traced back to the Gasserian 

 ganglion, and forwards to the point where it enters the 

 maxillary hiatus to pass through the infra- orbital canal and 

 emerge on the face at the infra- orbital foramen, where it 

 divides into numerous branches. In the orbit this nerve is 

 accompanied by the internal maxillary artery. 



Internal to the Superior Maxillary Branch, and between it 

 and the nerves to the Eye will be found the much difi'used 

 SphenO'Palatine Ganglion, also known as Meckel's Ganglion. 

 The junction of the Orbital branch with the Superior maxil- 

 lary division takes place about the middle of the ganglion. 



