of dark oblong bodies separated by light spaces of equal length; now, the dark bodies are each composed of a pair of cells containing the densest form of myo

STRUCTURE OF THE ULTIMATE MUSCULAR FIBRIL AND FIBRE OF ANIMAL LIFE. A. Ultimate muscular fibril in the state of partial contraction. B. The same in the state of ordinary relaxation. This fibril measured of an inch in diameter.. c. A similar fibril put upon the stretch, and measuring too of an inch in diameter. D. Plan of a portion of an ultimate fibre, showing the manner in which the transverse striæ are produced, by the collocation of the fibrils.

Nos. 1, 1. The pair of highly refractive cells; they form the dark parts of the single fibrils, but the bright parts of the fibre D. In the stretched fibril c, each cell has the appearance of being double. 2, 2. The pair of less refractive cells, light in the single fibrils, but forming the shaded striæ in D. The transverse septum between these cells is very conspicuous; and in c two other septa are seen to exist, making the number of transparent cells four. In D, the tier of cells immediately above the dark tier is partially illumined from the obliquity of the light. (By an error on the part of the engraver the boundary lines of the fibril are omitted in A B and c.)

line, and are hence highly refractive, while the transparent spaces are constituted by a pair of cells containing a more fluid myoline. When the fibrils are collected together so as to form an ultimate fibre or fasciculus, the appearance of the cell is altered; those which look dark in the single fibril, that is, the most refractive, being ranged side by side, constitute the bright band; while the transparent cells of the single fibril are the shaded striæ of the fibre.

When the ultimate fibril is very much stretched, the two highly refractive cells appear each to be double; while the transparent space is evidently composed of four cells.

The ultimate fibre of organic life, or smooth muscular fibre, is a single homogeneous filament much smaller than the fibre of animal life, flat, smooth, and without transverse markings. It is of a fusiform shape, and various length, and consists of a thin external membrane, blended with a soft, homogeneous or finely granular contained substance. These fibres were originally round nucleated cells, which have become elongated into a fusiform shape, and subsequently grown into the dimensions of fibres. When of small size they have a single nucleus; but in the longer fibre a succession of nuclei with corresponding swollen parts may be observed from point to point, and the nucleus is sometimes so much elongated as to deserve the title of columnar. The fusiform cells are united into little bundles or fasciculi by an adhesive interstitial substance, and the fasciculi, which are sometimes round and sometimes flat, are bound together into larger bundles by areolar tissue and fine elastic fibres; the interspaces of the bundles being occupied by vessels and nerves, the former in great abundance

Organic or smooth muscle is distributed abundantly in the animal frame, and is met with in all situations where a distinct contractile power, independent of mere elasticity, is required; for example, in the alimentary canal, from the middle. of the oesophagus to the internal sphincter ani; in the posterior segment of the trachea, and in the bronchial tubes to their finest ramifications; in the excretory ducts of various glands, as Wharton's duct, the ductus communis choledochus, the calices and pelves of the kidneys; the ureters, bladder, and urethra; on the testes, around the vasa deferentia and vesiculæ seminales, the prostate, Cowper's glands, and in the substance of the corpora cavernosa; in the Fallopian tubes, uterus and vagina; in the middle coat of arteries, veins, and lymphatic vessels; in the iris; and in the corium of the skin, particularly in the areola and nipples

of the mammary glands, in the dartos of the scrotum, and around the hair follicles, and many of the sudoriferous and sebiferous ducts.

FIG. 154.

B

ULTIMATE MUSCULAR FIBRE OF ORGANIC LIFE. A. Muscular fibre of or

ganic life from the urinary bladder, magnified 600 times, linear

measure. Two of the nuclei are seen. B. Mus

cular fibre of organic life, from the stomach, The diameter of this and the preceding fibre, midway between the nuclei,

magnified 600 times.

was of an inch.

The development of muscular fibre is effected by means of the formation of nucleated cells out of an original blastema, and the conversion of those cells into the tubuli of ultimate fibres, while their contents, by a subsequent developmental action, are transformed into ultimate fibrils. In the muscular fibre of organic life the process seems to stop short of the formation of fibrilla; the cellcontents retaining their original homogeneous or granular character.

Muscles are divided into two great classes, voluntary and involuntary, to which may be added, as an intermediate and connecting link, the muscle of the vascular system, the heart.

The voluntary, or system of animal life, is developed from the external or serous layer of the germinal membrane, and comprehends the whole of the muscles of the limbs and trunk. The involuntary, or organic system, is developed from the internal or mucous layer, and constitutes the thin muscular structure of the intestinal canal, urinary passages, and internal organs of generation. At the commencement of the alimentary canal at the middle of the oesophagus, and near its termination at the anus, the muscular coat is formed by a blending of the fibres of both classes. The heart is developed from the middle, or vascular layer of the germinal membrane; and although involuntary in its action is composed of ultimate fibres, having

the transverse striæ of the muscle of animal life. Striated muscle is also found around the vena cava near the heart, in the upper half of the oesophagus, and in the round ligaments of the uterus. THE MUSCLES may be arranged in conformity with the general division of the body into 1. Those of the head and neck. 2. Those of the trunk. 3. Those of the upper extremity. 4. Those of the lower extremity.

MUSCLES OF THE HEAD AND NECK.

The muscles of the head and neck admit of subdivision into those of the head and face, and those of the neck.

MUSCLES OF THE HEAD AND FACE.

These muscles may be divided into groups corresponding with the natural regions of the head and face; the groups are eight in number, namely,

5. Superior labial group.

6. Inferior labial group.
7. Maxillary group.
8. Auricular group.

The muscles of each of these groups may be thus arranged:

1. Cranial group.

Occipito-frontalis.

2. Orbital group.

Orbicularis palpebrarum,

Corrugator supercilii,
Tensor tarsi.

3. Ocular group.
Levator palpebræ,
Rectus superior,
Rectus inferior,

Rectus internus,

Rectus externus,

Obliquus superior,
Obliquus inferior.

4. Nasal group.

Pyramidalis nasi,

Compressor naris,

Dilatator naris,

Depressor alæ nasi,

[Levator labii superioris alæque nasi.] Levator labii inferioris.

Dissection. The occipito-frontalis is to be dissected by making a longitudinal incision along the vertex of the head, from the tubercle on the occipital bone to the root of the nose; and a second incision along the forehead and around the side of the head, to join the two extremities of the preceding. Dissect the integument and superficial fascia carefully outwards, beginning at the anterior angle of the flap, where the muscular fibres are thickest, and remove it altogether. This dissection requires care; for the muscle is very thin and without attention would be raised with the integument. There is no deep fascia on the face or head, nor is it required; for here the muscles are closely applied against the bones, upon which they depend for support, whilst in the extremities the support is derived from the dense layer of fascia by which they are invested, and which forms for each muscle a distinct sheath.

The OCCIPITO-FRONTALIS (epicranius) is a broad musculo aponeurotic layer, which covers the whole side of the vertex of the skull, from the occiput to the eyebrow. It arises by tendinous fibres from the outer two-thirds of the superior curved line of the occipital, and from the mastoid portion of the temporal bone. Its insertion takes place by means of the blending of the fibres of its anterior portion with those of the orbicularis palpebrarum, corrugator supercilii, levator labii superioris alæque nasi, and pyramidalis nasi. The muscle is fleshy in front over the frontal bone (frontalis) and behind over the occipital (occipitalis), the two portions being connected by a broad aponeurosis. The two muscles, together with their aponeurosis, cover the whole vertex of the skull, hence their designation galea capitis; they are loosely adherent to the pericranium, but closely to the integument, particularly on the forehead. At the side of the head the aponeurosis (galea aponeurotica) is attached to the root of the mastoid process and processus auditorius, and, becoming thin over the temporal fascia, is connected with the zygoma, malar bone, and external boundary of the orbit.

Relations. This muscle is in relation by its external surface with the frontal and supraorbital vessels, supraorbital and facial nerve, temporal vessels and auriculo-temporal nerve, occipital vessels and nerves, and integument, to which it is 1 [As this muscle belongs to two groups I have, following Mr. Wilson's plan, placed it in parentheses.]

The orbicularis oris, from encircling the mouth, belongs necessarily to both the superior and inferior labial regions; it is therefore inclosed within parentheses.

[This lateral portion, which is an extension from the edge of the proper tendon, is sometimes called the superficial temporal fascia.]

closely adherent. Its under surface is attached to the pericranium by a loose cellular tissue which admits of considerable movement.

MUSCLES OF THE HEAD AND FACE. 1. Frontal portion of the occipito-frontalis. 2. Its occipital portion. 3. Its aponeurosis. 4. Orbicularis palpebrarum, which conceals the corrugator supercili and tensor tarsi. 5. Pyramidalis nasi. 6. Compressor naris. 7. Orbicularis oris. 8. Levator labii superioris alæque nasi ; the adjoining fasciculus between ciphers 8 and 9 is the labial portion of the muscle. 9. Levator labii superioris proprius; the lower part of the levator anguli oris is seen between the muscles 10 and 11. 10. Zygomaticus minor. 11. Zygomaticus major. 12. Depressor labii inferioris. 13. Depressor anguli oris. 14. Levator labii inferioris. 15. Superficial portion of the masseter. 16. Part of its deep portion. 17. Attrahens aurem. 18. Buccinator. 19. Attollens aurem. 20. Temporal fascia covering the temporal muscle. 21. Retrahens aurem. 22. Anterior belly of the digastricus; the tendon is seen passing through its aponeurotic pulley. 23. Stylo-hyoid muscle pierced by the posterior belly of the digastricus. 24. Mylo-hyoideus. 25. Upper part of the sterno-mastoid. 26. Upper part of the trapezius. The muscle between 25 and 26 is the splenius.

Action.To raise the eyebrows, thereby throwing the integument of the forehead into transverse wrinkles. Some persons have the power of moving the entire scalp on the pericranium by means of these muscles.

Dissection. -The dissection of the face is to be effected by continuing the longitudinal incision of the vertex of the previous dissection onwards to the tip of the nose, and thence downwards to the margin of the upper lip; then carry an incision along the margin of the lip to the angle of the mouth, and transversely across the face to the angle of the lower jaw. Lastly, divide the integument in front of the external ear upwards to the transverse incision which was made for exposing the occipito-frontalis. Dissect the integument and superficial fascia carefully from the whole of the region included by these incisions, and the present and two following groups of muscles will be brought into view.

The ORBICULARIS PALPEBRARUM is a sphincter muscle, surrounding the orbit and eyelids, and consists of two portions, external and internal. The external or orbital portion, arises from a short tendon, tendo palpebrarum (tendo oculi), situated at the inner angle of the eye, from the nasal process of the superior maxillary and angular process of the frontal bone; it encircles the orbit and is inserted into the inner border of the orbit and lower border of the tendo palpebrarum, some of its fibres being continuous with the upper segment. The internal portion (palpebralis) forms a curved plane of fibres on the eyelids, thinner and paler than the orbital portion; externally these fibres are attached to the external palpebral ligament and border of the orbit, some being continuous with the orbital portion; internally they are attached to the borders of the lacus lachrymalis and tendo palpebrarum. The borders of the palpebralis nearest the edges of the lids

are thicker than the rest, and termed ciliaris. Mr. Haynes Walton' remarks that the ciliaris is redder than the rest of the palpebralis, and continuous with the tensor tarsi; he conceives it to be the active cause in the production of entropium.

The tendo palpebrarum (tendo oculi), about two lines in length and one in breadth, is attached by one end to the nasal process of the superior maxillary bone, close to the edge of the orbit; the other end bifurcates to be inserted into the inner extremities of the tarsal cartilages; from its inner side is given off a process which spreads over the lachrymal sac, and is attached to the crest of the lachrymal bone; this is the reflected aponeurosis of the tendo palpebrarum, and serves to protect the lachrymal sac.

Relations. By its superficial surface it is closely adherent to the integument, from which it is separated on the eyelids by a loose cellular tissue. By its deep surface it lies in contact, above, with the upper border of the orbit, corrugator supercilii muscle, frontal and supraorbital vessels, and supraorbital nerve; below, with the lachrymal sac, levator labii superioris alæque nasi, levator labii superioris proprius, zygomaticus major and minor muscles, and malar bone; externally, with the temporal fascia. On the eyelids it is in relation with the broad tarsal ligament and tarsal cartilages, and by its upper border is connected with the occipito-frontalis.

The CORRUGATOR SUPERCILII is a small, narrow, and pointed muscle, situated immediately above the orbit and beneath the upper segment of the orbicularis palpebrarum. It arises from the inner extremity of the superciliary ridge, and is inserted into the under surface of the orbicularis palpebrarum. Its connexion with the orbicularis commences near the supraorbital foramen and is continued outwards to the external angular process.

Relations. By its superficial surface, with the pyramidalis nasi, occipitofrontalis and orbicularis palpebrarum; by its deep surface, with the supraorbital vessels and nerve.

[FIG. 156.

1

The TENSOR TARSI (Horner's muscle) is a thin plane of muscular fibres, about three lines in breadth, and six in length. It is best dissected by separating the eyelids from the eye, and turning them over the nose without disturbing the tendo palpebrarum oculi; then dissect away the small fold of mucous membrane called plica semilunaris, and some loose cellular tissue under which the muscle is concealed. It arises from the orbital surface of the lachrymal bone, and passing across the lachrymal sac, divides into two slips, which are continuous with the margin of the ciliaris along the edges of the lids; some few of its fibres being attached to the lachrymal canals as far as the puncta. According to some anatomists the tensor tarsi is a process of the orbicularis consisting of two small fasciculi which inclose the lachrymal canals, and then spread out on the aponeurosis of the lachrymal sac to be inserted into the crest and orbital surface of the lachrymal bone.

A DIAGRAM OF THE TENSOR TARSI MUS

CLE. 1, 1. Bony margins of the orbit.
2. Palpebral fissure. 3. Orbital surface
the tensor tarsi.
of the lachrymal bone. 4. Origin of
5, 5. Insertion into
the neighborhood of the puncta lachry-
malia.]

Actions. The palpebral portion of the orbicularis acts involuntarily in closing

Medical Times and Gazette, May, 1852.

W. E. Horner, M.D., Professor of Anatomy in the University of Pennsylvania. The notice of this muscle is contained in a work published in Philadelphia in 1827, entitled Lessons in Practical Anatomy."

'Haynes Walton, loc. cit.