|Henry Gray (1825–1861). Anatomy of the Human Body. 1918.|
|from the medial palpebral ligament, and its deep surface is crossed by the lacrimal part of the Orbicularis oculi (page 380), which is attached to the crest on the lacrimal bone.|
Structure.—The lacrimal sac consists of a fibrous elastic coat, lined internally by mucous membrane: the latter is continuous, through the lacrimal ducts, with the conjunctiva, and through the nasolacrimal duct with the mucous membrane of the nasal cavity.
| The Nasolacrimal Duct (ductus nasolacrimalis; nasal duct).—The nasolacrimal duct is a membranous canal, about 18 mm. in length, which extends from the lower part of the lacrimal sac to the inferior meatus of the nose, where it ends by a somewhat expanded orifice, provided with an imperfect valve, the plica lacrimalis (Hasneri), formed by a fold of the mucous membrane. It is contained in an osseous canal, formed by the maxilla, the lacrimal bone, and the inferior nasal concha; it is narrower in the middle than at either end, and is directed downward, backward, and a little lateralward. The mucous lining of the lacrimal sac and nasolacrimal duct is covered with columnar epithelium, which in places is ciliated.|
FIG. 896– The lacrimal apparatus. Right side. (See enlarged image)
FIG. 897– Alveoli of lacrimal gland. (See enlarged image)
|1d. The Organ of Hearing|
(Organon Auditus; The Ear)
The ear, or organ of hearing, is divisible into three parts: the external ear, the middle ear or tympanic cavity, and the internal ear or labyrinth.
FIG. 898– Section through the head of a human embryo, about twelve days old, in the region of the hind-brain. (Kollmann.) (See enlarged image)
FIG. 899– Section through hind-brain and auditory vesicles of an embryo more advanced than that of Fig. 898. (After His.) (See enlarged image)
FIG. 900– Lateral views of membranous labyrinth and acoustic complex. X 25 dia. (Streeter.) absorpt. focu, area of wall where absorption is complete; amp., ampulla membranacea; crus, crus commune; d. sc. lat., ductus semicircularis lateralis; d. sc. post., ductus semicircularis posterior; d. sc. sup., ductus semicircular superior; coch. or cochlea, ductus cochlearis; duct. endolymph, ductus endolymphaticus; d. reuniens, ductus reuniens Henseni; endol. or endolymphs appendix endolymphaticus; rec. utr., recessus utriculi; sacc., sacculus; sac. endol., saccus endolymphaticus; sinus utr. lat., sinus utriculi lateralis; utric., utriculus; vestib. p., vestibular pouch. (See enlarged image)
The Development of the Ear.—The first rudiment of the internal ear appears shortly after that of the eye, in the form of a patch of thickened ectoderm, the auditory plate, over the region of the hind-brain. The auditory plate becomes depressed and converted into the auditory pit (Fig. 898). The mouth of the pit is