242 HEAD AND NECK 



ganglion. It, as has been mentioned already (p. 220), is formed by the 

 union of the tympanic branch of the glosso-pharyngeal with a branch 

 from the ganglion geniculi of the facial. 



External Superficial Petrosal Nerve. It is convenient at this stage to 

 take note of a fourth petrosal nerve the external superficial petrosal. It 

 takes origin from the sympathetic plexus which accompanies the middle 

 meningeal artery, and, entering the petrous bone, is conducted to the 

 ganglion geniculi of the facial nerve. 



Middle and Accessory Meningeal Arteries. The entrance 

 of the middle meningeal artery through the foramen spinosum 

 should now be examined. It gives minute twigs to the 

 semilunar ganglion, and one the superficial petrosal artery 

 which accompanies the greater superficial petrosal nerve 

 into the hiatus canalis facialis. The further course of the 

 middle meningeal artery has been described already (p. 118). 

 The nervus spinosus, from the mandibular nerve, also enters 

 the cranium through the foramen spinosum (p. 179). 



The accessory meningeal artery enters the cranium through 

 the foramen ovale, and is distributed chiefly to the semilunar 

 ganglion. 



THE ORBIT. 



Within the orbital cavity the following structures are 

 grouped around the eyeball and the optic nerve : 



'Rectus superior. 



Rectus inferior. 



Rectus lateralis. 

 Muscles, . ,\ Rectus medialis. 



Obliquus superior. 



Obliquus inferior. 

 ^Levator palpebrse superioris. 



Ophthalmic artery and its branches. 



Vessels, . . \ Ophthalmic veins (superior and inferior), with their tribu- 

 taries. 



Oculo-motor (3rd cerebral). 



Trochlear (4th cerebral). 



Abducent (6th cerebral). 



Nerves, . A T I from ophthalmic division of the trigeminal 



Naso^ry, J or fifth cerebral nerve. 

 Zygomatic branch of the maxillary division of the tri- 

 geminal nerve. 

 Ciliary ganglion. 

 Lacrimal gland. 

 Fascia Bulbi. 



Dissection. The roof of the orbit must be removed with 

 the aid of the saw, the chisel, and the bone forceps. Begin by 



