and downwards, and enters the sac near the other, behind the tendon of the orbicularis.

The LACHRYMAL SAC occupies a fossa formed by the superior maxilla and os unguis in the inner and anterior part of the orbit. It is continuous with the upper extremity of the ductus ad nasum, from which it is separated only by a constriction or fold of the mucous membrane. It is separated from the anterior extremity of the middle meatus of the nose by the lachrymal bone.

The DUCTUS AD NASUM, Fig. 7, f, leads from the lachrymal sac into the anterior extremity of the inferior meatus of the

LACHRYMAL APPARATUS AND NASAL DUCT.-a, b, c. Lachrymal gland and its appendage. d. Puncta lachrymalia. e. Lachrymal canals. f. Nasal duct laid open. g. Insertion of tendon of superior oblique muscle after being reflected. h. Supra-orbital foramen; the artery, vein, and nerve have been cut across. i. Interior of nasal duct near its termination in nostril.

It is directed downwards, backwards, and outwards; its osseous walls are composed of the superior maxilla, os unguis, and inferior turbinated bone. At is lower orifice there is a fold of mucous membrane which may serve as a valve. Its length is about three-fourths of an inch. Through the

lachrymal ducts, lachrymal sac, and nasal duct, the conjunctiva is continuous with the lining membrane of the nasal fossa; and as the former is prolonged into the lachrymal gland through its excretory ducts, there is a direct sympathetic connection established between that gland and the mucous membrane of the nose.

The appendages of the eye, which have just been described, deserve the careful attention of the student. They are frequently the seat of diseases which require surgical operations. A minute examination of the structure of the eyelids, and the lachrymal passages especially, is important.

SECT. III.-DISSECTION OF THE SOFT PARTS ON THE UPPER PART OF THE CRANIUM.

This region is included within the circumference of a line commencing just above the root of the nose, and extending round the head through the eyebrows, along the zygomatic arches, and just above the ears back to the occipital protuberance. It is subdivided into the Frontal, Temporal, Auricular, and Occipital regions. The parts to be studied in this dissection are: the integuments, the cellulo-adipose layer, the temporal fascia, the occipito-frontal muscle, the upper part of the orbicularis palpebrarum, the temporal muscle above the zygomatic arch, the attollens aurem, the attrahens aurem, the retrahens aurem, the cranial branches of the occipital, temporal, auricular, supra-orbital and facial arteries, and their corresponding veins, the cranial branches of the occipital, facial, and trifacial nerves, and the pericranium.

In removing the skin, an incision should be made from the root of the nose along the median line to the occipital protuberance, and another at right angles to this, extending down to the ear. The skin should then be dissected off in two flaps. The different layers which cover the cranium should be dissected on one side, and the nerves and vessels on the other. The integument which is covered with hair adheres closely to the cellulo-adipose layer, and some care is requisite to separate them.

The CELLULO-ADIPOSE LAYER is the thickest and most dense on the upper and posterior part of the head. Numerous

adipose cells are interspersed through it. The compactness of this structure, with its high degree of vitality, is said to be the cause of the tendency of the scalp to take on erysipelatous inflammation after injuries. When arteries are divided in its substance, the forceps instead of the tenaculum should be used in ligating them.

The OCCIPITO-FRONTAL MUSCLE, Fig. 61 (1, 2, 3), with its broad aponeurosis, extends from the root of the nose and the superciliary ridge to the superior transverse ridge of the occiput. It consists of two fleshy bellies connected by a broad aponeurosis, which expands over the arch of the cranium.

The OCCIPITAL PORTION arises from the superior transverse ridge of the occipital bone, and from the adjacent portion of the mastoid process of the temporal bone. The fibres pass upwards and somewhat inwards, and terminate in the tendon.

The FRONTAL PORTION is blended with the pyramidalis nasi, the orbicularis palpebrarum, and the integument; some of its fibres are also attached to the internal angular process of the frontal bone. It joins the tendon nearly opposite the coronal suture. Its fibres are generally paler than those of the occipital portion. The tendon of this muscle is continuous across the median line with that of the opposite side; and from its outer border, the superficial temporal fascia extends downwards over the deep temporal fascia or aponeurosis. The use of this muscle is to move the scalp, to raise the eyebrows, and, in some measure, the upper eyelids. It adheres closely to the scalp, while it glides freely on the parts beneath it. It causes the transverse wrinkles on the forehead.

The ATTOLLENS AUREM, Fig. 61 (4), is situated in the temporal region above the ear. It arises broad from the aponeurosis of the occipito-frontal muscle; its fibres converge as they descend, and are inserted into the concha of the ear. Its use is to raise the ear, and to render tense the aponeurosis from which it arises.

The ATTRAHENS AUREM, Fig. 61 (3), is situated immediately in front of the preceding muscle. It arises from the aponeurosis of the occipito-frontal muscle and the zygoma, and is inserted into the anterior part of the helix. It draws the ear upwards and forwards.

The RETRAHENS AUREM, Fig. 61 (6), is placed behind the ear. It generally consists of two or three fasciculi. It arises from the mastoid process, and is inserted into the posterior and lower part of the concha. It draws the ear backwards and enlarges the meatus. Having dissected the occipito-frontal muscle and the muscles of the ear, they should be removed. Beneath the occipito-frontal muscle, more or less loose areolar tissue will be observed, which facilitates the movements of that muscle on the pericranium. The pericranium is the external periosteum of the bones which it covers. It can be readily separated from the bone except along the sutures.

The student should now carefully study the different layers which have just been examined with reference to wounds involving one or more of them, and especially in view of collections of pus between the different layers, or beneath the pericranium.

The TEMPORAL APONEUROSIS occupies the whole of the temporal region. It arises from the temporal ridge above, and is attached below to the zygomatic arch. The lower part of it is divided into two layers, one of which is inserted into the outer, and the other into the inner border of the arch, thus leaving a triangular space between them, which is filled with adipose substance, and traversed by the Iniddle temporal artery, and a small branch of the superior maxillary nerve. The temporal muscle arises partly from the under surface of this aponeurosis. It will be observed, that if pus should collect beneath the temporal aponeurosis, it would naturally seek an outlet beneath the zygomatic arch; or, if it should collect between the two layers above the zygoma, it would necessarily be confined to that space.

The TEMPORAL MUSCLE, Fig. 64 (1), lies beneath the temporal aponeurosis. It arises from the whole of the temporal fossa and ridge, from the inner surface of the aponeurosis and from the zygomatic arch. Its fibres converge, and passing downwards beneath the zygoma, are inserted by a strong tendon into the coronoid process of the inferior maxilla. The muscle increases in thickness as it descends. When the entire muscle acts, it raises the lower jaw; the posterior fibres can move it backwards, while the anterior fibres can draw it forwards. This muscle may also assist in producing a rotary movement of the jaw.

It will be seen that the temporal aponeurosis and muscle, by their strength and thickness, serve greatly to protect that portion of the parietes of the cranium which they cover, and which in this region are very thin.

The vessels and nerves may now be dissected on the opposite side; and for this purpose, the integument should be raised in the same manner as for the dissection of the muscles and fasciæ.

The temporal and occipital, Fig. 1 (23, 20), are the principal arteries. Besides these, there are the terminal branches of the facial, the supra-orbital, and the posterior auricular. The nerves, Fig. 63, are derived from the fifth, the facial, and the cervical. To dissect the vessels and nerves, they should be traced from below upwards.

Entering the frontal region from below will be found the terminal branch of the facial artery, and the supra-orbital, and near these the supra-orbital and frontal nerves.

The SUPRA-ORBITAL ARTERY and NERVE pass through the supra-orbital foramen. The artery is distributed to the muscles and integument of this region. The nerve ascends beneath the orbicularis palpebrarum and occipitofrontal muscles, and some distance above the orbit divides into two cutaneous branches, which perforate the latter muscle, and ascend in long slender filaments to the top of the head. In its course it gives branches to the muscles beneath which it passes, and through which filaments are sent to the skin which covers the muscles.

The terminal branch of the FACIAL ARTERY supplies the parts above the root of the nose.

The FRONTAL NERVE is placed on the inner side of the supra-orbital, and has a similar course and distribution.

Besides the supra-orbital, the OPHTHALMIC ARTERY usually sends one or more small branches to the forehead.

The TEMPORAL ARTERY passes upwards over the zygoma, and close to the ear. It is accompanied by the auriculotemporal branch of the inferior maxillary division of the fifth pair of nerves. It divides into an anterior and a posterior branch. Just above the zygoma it gives off the middle temporal branch, which perforates the temporal aponeurosis.