II46 A MANUAL OF ANATOMY 



directed as to effectually prevent the reflux of chyle, and the flow 

 of blood, into it. The duct crosses the left vertebral artery, and 

 subsequently the left subclavian artery. 



Right Lymphatic Duct. — ^The position of this duct corresponds to 

 that of the thoracic duct on the left side. It is about | inch in 

 length, and is formed by the union of the right axillary lymphatic 

 trunk and right jugular lymphatic trunk. Besides returning 

 lymph from the right side of the head and neck and the right upper 

 limb, it receives the lymphatic vessels from the right side of the 

 heart, the right lung, the upper part of the right half of the thoracic 

 wall, and some of those from the supero-anterior surface of the 

 liver. It terminates in the angle of junction of the internal 

 jugular and subclavian veins of the corresponding side, its orifice 

 being guarded by a double valve. 



Cervical Portion of the Lung — The apex of the lung projects into 

 the root of the neck for from i to i^ inches. It is covered by the 

 dome of the pleura, on the inner and anterior aspects of which the 

 subclavian artery arches outwards. The dome of the pleura is 

 covered by Sibson's fascia, which extends from the internal border 

 of the first rib to the front of the transverse process of the Seventh 

 cervical vertebra. This fascia is probably derived from the adjacent 

 scalene muscles, and it may contain some muscular fibres. 



The Orbit. 



The contents of the orbit are as follows : (i) the eyeball and the 

 optic nerve ; (2) the capsule of Tenon ; (3) seven muscles, six of 

 which belong to the eyeball, namely, the four recti and two 

 obliqui, whilst the seventh belongs to the upper eyelid, and is 

 called the levator palpebrae superioris ; (4) the third, fourth, 

 and sixth cranial nerves, the three branches of the ophthalmic 

 division of the fifth cranial nerve, namely, frontal, lachrymal, and 

 nasal, and the orbital or temporo-malar branch of the superior 

 maxillary division of the fifth cranial nerve ; (5) the ciliary, len- 

 ticular, or ophthalmic ganglion ; (6) the lachrymal gland ; and 

 (7) a quantity of soft fat. The foregoing contents are surrounded 

 by a fibrous sheath which is formed by the periosteum. 



Periosteum. — ^The periosteum of the orbit is continuous pos- 

 teriorly with the dura mater through the sphenoidal fissure. An- 

 teriorly it becomes continuous with the pericranium of the frontal 

 bone, and the periosteum of the superior maxillary and malar 

 bones. Along the supra-orbital and infra-orbital margins the 

 superior and inferior palpebral ligaments blend with it. The 

 periosteum is loosely attached to the bony walls of the orbit, and 

 forms a sheath for the contents of the cavity, which is incomplete 

 in front. 



Lachrymal Gland. — This gland lies at the anterior and outer 

 part of the orbit superiorly, where it occupies the lachrymal fossa 

 on the inner side of the external -angular process of the frontal 



