DISSECTION OF THE ORBIT 333 



be found to enter the foramen lacerum, where it joins the 

 nervus petrosus profundu s from the carotid plexus. The trunk 

 formed by the union of these two filaments is the nervus 

 canalis ptcrygoidei (O.T. Vidian nerve}. 



Nervus Petrosus Superficialis Minor appears upon the anterior face 

 of the petrous bone, through an aperture which is placed immediately 

 lateral to the hiatus canalis facialis. It leaves the cranial cavity by passing 

 downwards between the great wing of the sphenoid and the petrous part 

 of the temporal bone, or through the canaliculus innominatus or through 

 the foramen ovale, to reach the otic ganglion. This minute nerve, as 

 has been mentioned already (p. 312), 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 petrosal artery which 

 accompanies the great superficial petrosal nerve into the 

 hiatus canalis facialis. The further course of the middle 

 meningeal artery has been described already (pp. 220). 

 The nervus spinosus of the mandibular nerve also enters 

 the cranium through the foramen spinosum (p. 275). 



The accessory meningeal artery enters the cranium through 

 the foramen ovale, and is distributed chiefly to the semilunar 

 ganglion. 



DISSECTION OF THE ORBIT. 



Within the orbital cavity the following structures are 

 grouped around the eyeball and the optic nerve : 



Muscles, 



Rectus superior. 

 Rectus inferior. 

 Rectus lateralis. 

 Rectus medial is. 



Obliquus superior. 

 Obliquus inferior. 

 Levator palpebrae superioris. 

 ( Ophthalmic artery and its branches. 



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

 taries. 



