i4 PRACTICAL ANATOMY. 



artery, and the lachrymal nerve, a branch of the ophthalmic division of the fifth 

 nerve, lying on the external rectus muscle. 



3. To the inner side we saw the fourth nerve, called also the patheticus, 

 lying on and supplying the superior oblique muscle with motion, in its course 

 having passed above the levator palpebrae muscle and the frontal nerve. 



Describe the frontal nerve, which you found on t/ie levator palpebrce, and tell 

 what structure intervened bet'cvcen the periorbita and this nerve. 



The intervening structure was the peripheral part of the orbital fascia. It was 

 so thin and translucent that we could see the nerve through the fascia. The 

 frontal nerve is a branch of the ophthalmic part of the fifth nerve. About midway 

 between the optic foramen and the supraorbital foramen it divides into a supra- 

 orbital and a supratrochlear branch. The supraorbital branch leaves the orbit 

 through the supraorbital foramen and supplies the skin of the upper lid, the 

 skin of the forehead, and the pericranium in this same region ; the supratroch- 

 lear branch communicates with the infratrochlear branch of the nasal nerve 

 around the pulley for the superior oblique muscle, branches being given off 

 from this loop to supply the upper lid, forehead, and nose. 



Describe the lachrymal nerve, which you saw on the external rectus muscle. 



It is a branch of the ophthalmic part of the fifth nerve. It gives branches to the 

 lachrymal gland, and to the skin and mucous membrane of the upper lid, and sends 

 a communicating branch to the orbital branch of the superior maxillary nerve. 



Describe the nasal nerve. 



It is a branch of the ophthalmic. It has a most complicated course, which 

 to be learned thoroughly must be studied according to these stages : 



1. The nerve enters the orbital cavity by the sphenoidal fissure. 



2. In its course through the orbit it passes : (i) Between the optic nerve and 

 superior rectus muscle ; (2) between the external rectus muscle and the superior 

 oblique muscle, and arrives at the anterior ethmoidal foramen. In this, its 

 orbital stage, the nerve gives off the long root to the ciliary ganglion, at the 

 sphenoidal fissure, and the long ciliary nerves to the eyeball, as it crosses the optic 

 nerve. At the anterior ethmoidal foramen the nerve gives off the infratrochlear 

 branch, to communicate with the supratrochlear branch of the frontal nerve. 



3. In company with the anterior ethmoidal artery it enters the cranial cavity, 

 by the anterior ethmoidal foramen, crosses the cribriform plate of the ethmoid 

 bone, and leaves the cranial cavity and gains the nasal cavity by the nasal slit, by 

 the side of the crista galli. 



4. The nerve divides in the nasal cavity into septal branches, which are dis- 

 tributed to the upper and front part of the septum nasi, and branches to the 

 outer wall and anterior ends of the two lower turbinals. The end branch of this 

 nerve passes between the cartilage and the end of the nasal bone, supplying the 

 tip and lobe of the nose. 



Describe the motor oculi, or third cranial nerve. 



This nerve is the most important motor nerve to the muscles of the orbit. 

 As the nerve emerges from the cavernous sinus it divides into a superior and 

 an inferior division, which enter the orbit by the sphenoidal fissure. The 

 superior division supplies the levator palpebrae and superior rectus muscles. 

 The inferior division supplies the internal rectus, the inferior rectus, and the 

 inferior oblique. The third nerve supplies with motion the circular fibres of the 

 iris and the ciliary muscle, through the ciliary ganglion. 



Describe the fourth crania! nerve. 



It is called patheticus and trochlear. It enters the orbit by the sphenoidal 

 fissure, passes above the frontal nerve and levator palpebras muscle, and is 

 distributed to the superior oblique muscle. This is the smallest of the cranial 

 nerves. 



