THE HEAD AND NECK ii47 



bone. It is almond-shaped. Its upper surface is convex, and 

 its under surface is concave in adaptation to the eyeball. The 

 anterior part of the gland is more or less detached, and is known 

 as tlie palpebral portion, the chief part being known as the orbital 

 portion. The ducts, which issue from both portions, are about 

 twelve in number, and they open in a row into the outer part of 

 the superior fornix conjiinctivce. 



Blood-supply. — ^The lachrymal artery. 



Nerve-supply. — ^The lachrymal nerve, and sympathetic filaments. 



The structure of the gland is similar to that of the parotid gland. 



Development. — The lachrymal gland, hke the Meibomian glands and glands 

 of Moll, is developed as solid epitheUal cords from the conjunctiva. The solid 

 epithelial cords spring from the upper and outer part of the conjunctiva, 

 where it is reflected from the inner surface of the upper eyelid on to the front 

 of the eyeball. The solid cords grow into the contiguous mesoderm, and give 

 off lateral processes. Cords and processes, at first solid, soon become hollow, 

 and so give rise to the alveoU, or acini, and ducts of the lachrymal gland. 



Muscles. — These are seven in number, as follows : levator pal- 

 pebrae superioris, superior rectus, inferior rectus, internal rectus, 

 external rectus, superior oblique, and inferior oblique. 



Levator Palpebrse Superioris — Origin. — ^The under surface of the 

 roof of the orbit above, and in front of, the optic foramen. 



Insertion. — By a broad membranous expansion, which divides 

 into three layers. The middle layer, which represents the chief 

 insertion, and consists largely of involuntary muscular fibres, is 

 attached to the upper margin of the superior tarsal plate. The 

 upper or superficial layer, which is fibrous, passes over, or in front 

 of, the superior tarsal plate, lying between it and the palpebral 

 fibres of the orbicularis palpebrarum. Its fibres pierce the superior 

 palpebral ligament, and, having passed between the bimdles of the 

 palpebral portion of the orbicularis palpebrarum, they are attached 

 to the skin of the upper eyelid. The lower or deep layer, which is 

 also fibrous, is attached to the conjunctiva along the superior fornix. 

 The outer and inner margins of the broad membranous expansion 

 are attached to the outer and inner margins of the orbit close to 

 the external and internal tarsal ligaments, and at the inner angle 

 a slip is detached to the pulley of the superior oblique muscle. 



Nerve-supply. — ^The upper division of the third cranial nerve, the 

 branch from which enters the deep or ocular surface of the muscle 

 near its origin. 



Action. — To raise the upper eyelid. The muscle is the antagonist 

 of the superior palpebral fibres of the orbicularis palpebrarum. 



Relations. — Superiorly, the frontal ner\'e and the supra-orbital 

 artery. Inferiorly, the superior rectus and the conjunctiva. 



Recti Muscles — Superior Rectus — Origin. — ^The upper part of the 

 fibrous ring in relation to the optic foramen. 



Insertion. — By a thin expanded tendon into the upper surface 

 of the sclerotic about three or four lines from the margin of the 

 cornea. 



