Dissection of Sheep* s Head. 239 



belly of the external pterygoid ; in other words, through the 

 Frontal, anterior margin of Parietal, and Sphenoid bones, in 

 the direction of the sphenoidal fissure ; and here care must 

 be taken not to saw through too deep, or otherwise the second 

 subdivision of the Trifacial, which goes horizontally forwards 

 from the sphenoidal fissure, viz., the Superior Maxillary 

 subdivision, will be injured or even cut through. The posterior 

 incision should be made on a line drawn from a point about 

 two inches in advance of the posterior margin of the occipital 

 condyle, through the glenoid fossa, down to the upper surface 

 of the Inferior Maxillary nerve ; in other words, from the 

 upper margin of the occipital bone to the foramen ovale, 

 keeping clear of, and to the front of the external auditory 

 meatus and glasserian fissure, so as to leave the Chorda tym- 

 pani uninjured. Neither of these incisions should be carried 

 with the saw quite down to the points indicated ; but when 

 within a short distance thereof, a few strokes with the mallet 

 on the outer table of the part to be removed, will complete 

 the fracture along the line of the foramina required; and 

 then by carefully scraping the dura mater from the inner 

 surface of the bones with ,the scalpel, the portion of the 

 cranial wall may be removed without injury to the nervous 

 structures lying just within. 



Removal of Posterior Margin, and Superior Internal 

 Wall of Orbit, and Dissection of Orbital Membrane and 

 Lachrymal Gland. Three cuts should he made with the saw; 

 one just below the junction between the frontal and malar 

 bones ; a second a little distance, about three-eighths of an 

 inch, above this point ; and a third along a line drawn from 

 the anterior margin of the orbit to the Optic nerve where it 

 leaves the skull through the optic foramen. This last incision 

 must not be made too near the middle line of the skull or the 

 pulley of the superior oblique muscle will be destroyed. The 

 Student, with the skull before him, will bear in mind through 



