ANATOMY EN A NUTSHELL. 531 



Insertion. — Into the sclerotic coat three of tour lines from the sclero- 

 corneal junction. 



Action. — Abducts the cornea. 

 Nerve Supply. — Thin I nerve. 

 Blood*Supply. — Muscular branches of the ophthalmic artery. 



10. External rectus. — Description. — This is the largesl of the Recti 

 muscles. 



Origin. — From two heads. The outer head from the outer margin of the 

 optic foramen. The lower head from the ligament of Zinn and the lower 

 margin of the sphenoidal fissure. 



Insertion. — Into the sclerotic coat. 



Action. — It abducts the cornea. 



Nerve Supply. — The sixth nerve. 



Blood Supply. — Muscular branches from the ophthalmic artery. 



All the structures on the floor of the sphenoidal fissure are between the 

 two heads of the External rectus muscle, namely, ophthalmic vein, sixth. two 

 divisions of the third, and the nasal branch of the fifth nerves. 



11. Internal rectus. — Description. — This is the broadest of the meet 

 muscles. 



Origin. — From the ligament of Zinn. 



Insertion. — Into the sclerotic coat. 



Action. — It adducts the cornea. 



Nerve Supply. — From the inferior division of the third cranial nerve. 



Blood Supply. — Muscular branches of the ophthalmic artery. 



12. Laxator tympani, so-called by Sommeriny, is now called the anterior 

 ligament of the malleus. It is attached tuthe neck of the malleus and to the 

 anterior wall of the tympanum, with some of its fibers passing through Glas- 

 erian fissure to the spine of the sphenoid bone. 



LESSON CLXXIX. 

 Nasal Bone. (Plate CCL). 



The nasal bone, which with its fellow forms the bridge of the nose, is a 

 bone with two surfaces and four borders. It is situated at the upper part of 

 the face. 



The outer surface is convex transversely, but concave from above down- 

 wark. It has many small furrows for arteries, and at its center a foramen for 

 a vein. This foramen may be double. 



The inner surface is jus! the reverse of the ohter surface, which makes it 

 concave transversely and convex from above downward. There i- a longi- 

 tudinal groove on this surface for a branch of the nasal nerve. 



The superior border articulates with the nasal notch of the frontal bone. 

 It is serrated, thick, ami narrow. 



The inferior border is thinner and broader than the superior border, ami 

 gives attachment to the lateral cartilage. There is a notch at its middle for 

 the branch of the nasal nerve. 



The external border articulate- with the nasal process of the superior 

 maxillary bone. 



