628 ORGANS OF THE SENSES. 



The lachrymal gland is lodged in a depression at the outer angle of the orbit, 

 on the inner side of the external angular process of the frontal bone. It is of an 

 oval form, about the size and shape of an almond. Its upper convex surface is in 

 contact with the periosteum of the orbit, to which it is connected by a few fibrous 

 bands. Its under concave surface rests upon the convexity of the eyeball, and 

 upon the Superior and External recti muscles. Its vessels and nerves enter its 

 posterior border, whilst its anterior margin is closely adherent to the back part 

 of the upper eyelid, and is covered, on its inner surface, by a reflection of the 

 conjunctiva. This margin is separated from the rest of the gland by a slight 

 depression, hence it is sometimes described as a separate lobe, called the palpe- 

 bral portion of the gland. In structure and general appearance, it resembles the 

 salivary glands. Its ducts, about seven in number, run obliquely beneath the 

 mucous membrane for a short distance, and, separating from each other, open by a 

 series of minute orifices on the upper and outer half of the conjunctiva, near its 

 reflection on to the globe. These orifices are arranged in a row, so as to disperse 

 the secretion over the surface of the membrane. 



The lachrymal canals commence at the minute orifices, puncta lacrymalia, 

 seen on the margin of the lids, at the outer extremity of the lacus lacrymalis. 

 They commence on the summit of a slightly elevated papilla, the papilla lacry- 

 malis, and lead into minute canals, the canaliculi, which proceed inwards to 

 terminate in the lachrymal sac. The superior canal, the smaller and longer of 

 the two, at first ascends, and then bends at an acute angle, and passes inwards and 

 downwards to the lachrymal sac. The inferior canal at first descends, and then, 

 abruptly changing its course, passes almost horizontally inwards. They are dense 

 and elastic in structure, and somewhat dilated at their angle. 



The lachrymal sac is the upper dilated extremity of the nasal duct, and is 

 lodged in a deep groove formed by the lachrymal bone and nasal process of the 

 superior maxillary. It is oval in form, its upper extremity being closed in and 

 rounded, whilst below it is continued into the nasal duct. It is covered by the 

 Tensor tarsi muscle and by a fibrous expansion derived from the tendo oculi, 

 which is attached to the ridge on the lachrymal bone. In structure, it consists of 

 a fibrous elastic coat, lined internally by mucous membrane ; the latter is continuous, 

 through the canaliculi, with the mucous lining of the conjunctiva, and through the 

 nasal duct with the pituitary membrane of the nose. 



The nasal duct is a membranous canal, about three quarters of an inch in 

 length, which extends from the lower part of the lachrymal sac to the inferior 

 meatus of the nose, where it terminates by a somewhat expanded orifice, provided 

 with an imperfect valve formed by the mucous membrane. It is contained in an 

 osseous canal, formed by the superior maxillary, the lachrymal, and the inferior 

 turbinated bones, is narrower in the middle than at each extremity, and takes a 

 direction downwards, backwards, and a little outwards. It is lined by mucous 

 membrane, which is continuous below with the pituitary lining of the nose. In 

 the canaliculi, this membrane is provided with scaly epithelium; but in the 

 lachrymal sac and nasal duct, the epithelium is ciliated as in the nose. 



THE EAR. 



The Organ of Hearing consists of three parts ; the external ear, the middle ear 

 or tympanum, and the internal ear or labyrinth. 



EXTERNAL EAR. 



The External Ear consists of an expanded portion named the pinna or auricle, 

 and the auditory canal or meatus. The former serves to collect the vibrations of 

 the air constituting sound, and the latter conducts those vibrations to the tym- 

 panum. 



The pinna or auricle (fig. 311) consists of a layer of cartilage, covered by 

 integument, and connected to the commencement of the auditory canal ; it is of an 



