angle of the eye it forms a vertical semilunar fold, the plica semilunaris. The folds formed by the passage of the conjunctiva from the lids to the eyeball are called the superior and inferior palpebral folds, the former being the deeper; they contain numerous convoluted mucous glands, some of which resemble lymphoid follicles.

The ocular conjunctiva is thin, transparent, possesses few vessels in health, and is loosely attached to the globe by the subconjunctival areolar tissue.

The corneal conjunctiva consists only of epithelium.

5

What is the caruncula lacrimalis (Fig. 141)?

It is a small, conical, reddish body, at the inner canthus, occupying the space called the lacus lacrimalis, and is formed of a group of follicles, sebaceous and sweat-glands, covered with skin; from the caruncle project a few slender hairs.

Describe the lacrimal apparatus.

It consists of the lacrimal gland with its ducts, the canaliculi, the lacrimal sac, and the nasal duct.

The

Lacrimal gland' (Fig. 140) is an oval, compound racemose gland of the size and shape of an almond, lodged in a depression at the upper, outer portion of the orbit, its concave under surface resting upon the globe of the eye, the conjunctiva, superior and external recti muscles intervening; it is held in contact with the orbital periosteum by a few fibrous bands; it has two parts, the smaller one called the inferior lacrimal gland. It has never more than twelve

Ducts, opening by minute orifices in a row on the upper and outer part of the conjunctival fornix.

Tears are taken up by the puncta, thence passing through the canaliculi into the lacrimal sac and nasal duct, thus reaching the inferior meatus of the nose.

Describe the canaliculi.

They are two minute canals' about one-half a line in diameter, commencing at the puncta; the superior passing upward, then bending acutely to pass inward to the lacrimal sac; the inferior passing downward, then upward and inward; they are lined with mucous membrane continuous with the conjunctiva, and are one-third of an inch long (8 to 9 mm.).

What is the lacrimal sac2 (Fig. 141)?

It is the flattened, ovoidal, sacciform dilatation of the upper part of the nasal duct, lodged in the groove formed by the lacrimal bone and nasal process of the superior maxillary; its walls are formed of fibrous tissue covered internally by the

tensor tarsi muscle, and in front is the tendo oculi attached to the ridge of the lacrimal bone. When distended it is 15 mm. long and 5 or 6 mm. wide.

Describe the nasal duct3.

It is a membranous canal about three-fourths of an inch long (12 to 24 mm.), extending from the termination of the lacrimal sac through the osseous nasal duct to the inferior meatus of the nose, passing in a direction downward, backward, and slightly outward, its lumen being narrowest about the midpoint; externally it is composed of fibro-areolar tissue; internally, of mucous membrane continuous with that of the nose and lacrimal sac; the epithelial coating of the sac and duct is columnar and ciliated only in spots; squamous in the canaliculi.

What is the valve of Hasner?

An imperfect valve of mucous membrane guarding the somewhat expanded terminal opening of the duct into the inferior meatus of the nose; other valvular folds are less constant.

The Ear.

Where is the auditory apparatus lodged?

In the petrous, mastoid, and tympanic portions of the temporal bone.

The External Ear.

What is the auricle or pinna?

Its foundation is an expanded layer of fibro-cartilage, so disposed in ridges as to concentrate and direct the waves of sound into the external auditory meatus, to which it is attached; the cartilage is deficient at certain points where it is connected by fibrous tissue; it is covered with perichondrium, outside of which is thin, firmly adherent skin, containing sweat- and sebaceous glands, and provided with short downy hairs. The various ridges and depressions are as follows: the

Concha, the deep cavity leading into the meatus; the

Tragus, the pointed prominence in front of the concha projecting back over the meatus, bearing on its under surface tufts of hair; the

Antitragus, a small tubercle opposite the tragus, separated by a deep notch, the incisura intertragica; the

Helix, the external prominent margin of the auricle rising near the tragus; the

Antihelix, a parallel prominence anterior to the former, rising below at the antitragus, bifurcating above to form the Fossa of the antihelix, a triangular depression; the

Fossa of the helix, the narrow, curved depression between the helix and the antihelix (fossa scaphoidea).

An ear-point, or tubercle of Darwin, is occasionally seen on the postero-superior margin of the helix pointing forward; it is constant in the human embryo, and permanent in many monkeys.

The inferior, soft pendulous portion, formed of fat and connective tissue enclosed by integument, is the lobule of the ear. Describe the muscles of the external ear.

The attollens aurem, attrahens aurem, and retrahens aurem have been described on page 142; these are extrinsic; the intrinsic are the muscles of the auricle, but slightly developed in man; their motor nerve is the facial.

Helicis major: a narrow vertical band on the anterior border of the helix;

Helicis minor: an oblique band at the root of the helix from the concha ;

Tragicus: a short, vertical band on the outer surface of the tragus;

Antitragicus: stretching from the outer part of the antitragus to the lower part of the helix; these four muscles are anterior. Transversus auriculæ radiating from the posterior surface of the convexity of the concha to the prominence caused by the groove of the helix;

Obliquus auris a few fibers passing from the upper back part of the concha to the convexity immediately above.

Give the vascular and nerve-supply to the auricle.

The arteries are Posterior auricular, from the external carotid. Anterior auricular, branch of the temporal. Auricular, branch of the occipital.

The veins accompany the corresponding arteries.

The nerves are Auricularis magnus, from the cervical plexus. Posterior auricular, from the facial.

Auricular branch (Arnold's) of the

gastric.

pneumo

Auriculo-temporal, from the inferior maxillary division of the fifth nerve. Occipitalis major and minor.

What is the external auditory canal?

It is an osseo-cartilaginous, oval, cylindrical canal, with its greatest diameter vertical at the external orifice, but reversed

at the tympanic end; it is narrowest at the middle. About one inch long (25 mm.), it is directed obliquely forward and inward, and slightly curved with its convexity upward, and is lined with thin adherent skin, containing hair-follicles and sebaceous and ceruminous glands in its cartilaginous portion. A narrow groove for the membrana tympani is at the inner end, called the sulcus tympanicus, interrupted above by the notch of Rivinus between the anterior and the posterior tympanic spines.

What are the arteries and nerves?

The arteries are branches of the posterior auricular, internal maxillary, and temporal.

The nerves come chiefly from the auriculo-temporal branch of the third division of the fifth nerve and from the auricular branch of the vagus.

The Middle Ear or Tympanum.

Describe the membrana tympani.

It forms the outer wall of the tympanum, and is an oval, translucent membrane placed obliquely at the bottom of the external auditory meatus, with its internal surface facing downward, forward, and inward at an angle of 55°, with its long axis directed downward and inward; it inclines toward the anterior and lower part of the canal; at its upper anterior border is a white, pointed tubercle, formed by the short process of the malleus, while a yellowish-white stripe passing from this downward and backward toward the center indicates the handle of the malleus. During life, when illuminated, the membrana tympani presents a triangular light spot or "cone of light,” having its apex at the end of the malleus handle, whence it spreads downward and forward; a darker central portion is the umbo, or shadow. The upper anterior part bridging a small notch in the bony ring to which the membrane is attached (the notch of Rivinus), is thin, consisting of loose connective tissue, vessels, and nerves, covered with skin and mucous membrane, and has received the name of the membrana flaccida, or Shrapnell's membrane.

Of what tissues is the membrana tympani composed?

Of the skin, which is derived from the lining of the meatus;