I.] DISSECTION OF A RABBIT AND OF A DOG. 31 



of the Eustachian tube, pass a probe up it into 

 the tympanic cavity. Pass another probe down 

 the meatus extemus and, rupturing the mem- 

 brana tympani, make sure that the first probe 

 has entered into the tympanic cavity. 



25. Kemove one eye from its orbit, cutting through 

 the tissues close to the eye. In the anterior part 

 of the orbit note the white Harderian gland ; 

 in the anterior lower part the pale red infra- 

 orbital gland, the duct of which opens into the 

 mouth near the upper molars ; and the lachry- 

 mal gland pale-red like the infra-orbital in 

 the posterior part of the orbit. Observe the 

 point of entrance of the optic nerve into the 

 orbit. 



In the dog the muscles of the globe of the eye may 

 be dissected out, after removing with bone 

 forceps the roof of the orbit. 



26. Immediately below, and in front of the eye, 

 the superior maxillary nerve will be found 

 issuing from a foramen in the superior maxillary 

 bone, to supply the skin of the face, &c., with 

 sensory fibres. Cutting away the bone with a 

 small pair of bone forceps, trace this nerve back 

 along the floor of the orbit. 



27. In the upper part of the orbit of the dog note 

 the ophihalmio nerve. It passes from the front 

 of the orbit to the forehead. 



28. The superior and the inferior maxillary nerves 

 and the ophthalmic, when traced back, will be 

 found to unite into one large nerve, the fifth or 



