Dissection ofSheep^s Head. 241 



to the optic foramen and sphenoidal fissure. This reddish 

 mass* may be seen under a quarter-of-an-inch object glass, to 

 be composed for the most part of flat, pale, non-striped fibres, 

 collected together in bundles, with which is mingled both 

 white and yellow ordinary fibrous tissue : the pale non- 

 striped fibres having all the characters of the involuntary 

 muscular fibre. By irritation of the cervical sympathetic, 

 these membranes project the contents of the orbit, especially 

 the bulb, forwards. Retraction is produced by the trans- 

 versely-striped ^ retractor '. In Man, the orbital membrane 

 is much reduced in size, and the * retractor' is wanting, so 

 that no distinct projection of the bulb follows irritation of 

 the sympathetic! . 



The pink glandular mass, situated in the upper and back 

 part of the orbit, is the Lachrymal gland, which secretes the 

 tears ; it resembles in structure the saKvary glands ; and has 

 numerous fine ducts which open on the inner surface of the 

 upper eyelid. As the eyelids are generally removed with the 

 skin before the head is sent in to the market, their arrange- 

 ment can only be seen in a specimen specially reserved. 



Removal of Okbital Membrane and Dissection of the 

 Nerves, Ganglion, and Muscles contained therein. 

 The orbital membrane should be now divided towards the bach 

 of the orbit, and taken away ; and then the fat internal to 

 the membrane carefully removed : by this means the fine 

 Fourth nerve, which was traced before along the commence- 

 ment of the Ophthalmic branch of the Fifth nerve, may be 

 followed up to the inner side of the orbital cavity, and to its 

 termination in a muscle there situated. This muscle, by the 

 entrance of the Fourth nerve into it, is recognised as the 

 Superior Oblique muscle. It will be seen that the Fourth 



* If specially prepared by soaking in diluted nitric acid, 

 t Turner (Edinburgh), Natural History Eeview, January, 1862 ; and Strange- 

 way's Veterinary Anatomy, p. 475. 



I I 



