50 DISSECTION OF THE ORBIT. 



The CERVICO-FACIAL is smaller than the other trunk, and distributes 

 nerves to the lower part of the face and the upper part of the neck. It- 

 highest branches join the lowest offsets of the temporo-facial nerve, and 

 thus complete the network on the face. This trunk, whilst in the parotid, 

 jrives twigs to the gland, and is united with the great auricular nerve. 

 The terminal branches distributed from it are, buccal, supra-maxillary, 

 and infra-maxillary. 



The buccal branches pass forwards towards the angle of the mouth, 

 giving offsets to the buccinator muscle, and terminate in the orbicularis 

 oris. On the buccinator they join the branch ( 12 ) of the inferior maxillary 

 nerve to that muscle. 



The supra-maxillary branches course inwards above the base of the 

 lower jaw to the middle line of the chin, and supply the muscles and the 

 integument between the chin and mouth. Beneath the depressor anguli 

 oris the branches of the facial join offsets of the labial branch of the in- 

 ferior dental nerve ( 13 ) in their course to the middle line. 



The infra-maxillary branches lie below the jaw, and are distributed to 

 the upper part of the neck. The anatomy of these nerves will be given 

 with the dissection of the anterior triangle of the neck. 



SECTION IV. 



DISSECTION OF THE ORBIT. 



Directions. The orbit should be learnt on that side on which the mus- 

 cles of the face have been seen. 



Position. In the examination of the cavity the head is to be placed in 

 the same position as for the dissection of the sinuses of the base of the 

 skull. 



Dissection. For the display of the contents of the orbit, it will be neces- 

 sary to take away the cotton wool from beneath the eyelids. To remove 

 the bones forming the roof of the space, two cuts may be made with a saw 

 through the margin of the orbit, one being placed at the outer, the other 

 near the inner angle of the cavity ; and these should be continued back- 

 ward with a chisel, along the roof of the orbit, so as to meet near the optic 

 foramen. The piece of bone included in the incisions is now to be tilted 

 forwards, but is not to be taken away. 



Afterwards the rest of the roof of the orbit, which is formed by the 

 small wing of the sphenoid bone, is to be cut away with the bone forceps, 

 except a narrow ring around the optic foramen ; and any overhanging 

 bone on the outer side, which may interfere with the dissection, may be 

 likewise removed. During the examination of the cavity the eye is to 

 be pulled gently forwards. 



The periosteum of the orbit, which has been detached from the bone in 

 the dissection, surrounds the contents of the orbital cavity, and joins the 

 dura mater of the brain through the sphenoidal fissure. It encases the 

 contents of the orbit like a sac, and adheres but loosely to the bones. 

 Apertures exist posteriorly in the membrane for the entrance of the dif- 

 ferent nerves and vessels ; and laterally prolongations of the periosteum 

 accompany the vessels arid nerves leaving the cavity. 



