THE TEMPORAL BONES.

Borders.-The superior border is thin, bevelled at the expense of the internal surface, so as .to overlap the lower border of the parietal bone, forming the squam¬ous suture. The anterior inferior border is thick, serrated, and bevelled, alter¬nately at the expense of the inner and outer surfaces, for articulation with the great wing of the sphenoid.

. The Mastoid Portion  is situated at the posterior part of the bone; its outer surface is rough, and gives attachment to the Occipito-frontalis and Retrahens aurem muscles. It is perforated by numerous foramina; one of these, of large size, situated at the posterior border of the bone, is termed the mastoid foramen; it transmits a vein to the lateral sinus and a small artery from the occipital to supply the dura mater. The position and size of this foramen are very variable. It is not always present; sometimes it is situated in the occipital bone or in the suture between the temporal and the occipital. The mastoid portion is continued below into a conical projection, the mastoid process, the size and form of which vary somewhat. This process serves for the attachment of the Sterno-mastoid, ~Jllenius capitis, and 'rl'achelo-mastoid muscles. On the inner side of the mastoid process is a deep groove, the digastric fossa, for the attachment of the Diga"tric muscle; and, running parallel with it, but more in¬ternal, the occipital gronee. which lodges the occipital artery. The internal surface of the mastoid portion presents a deep, curved groove

. The groove for the lateral sinus is separated from the innermost of the mastoid air-cells by only a thin lamina of bone, and even this may be partly deficient. A section of the mastoid process shows it to be hollowed out into a number of cellular spaces, communicating with each other. called the mastoid cells, which exhibit the greatest possible variety us to their size and number.

THE INTERNAL EAR.

The bony canal of the cochlea  takes two turns and three-quarters round the modiolus. It is a little over an inch in length (about 30 mm.), and
diminishes gradually in size from the base to the summit, where it terminates in a cul-de-eac, the cupola, which forms the apex of the cochlea. The commence¬ment of this canal is about the tenth of an inch in diameter: it diverges from the modiolus toward the tympanum and vestibule, and presents three openings. One, the fenestra rotunda, communicates with the tympanum; in the recent state this aperture is closed by a membrane, the membrana tympani secundaria. Another aperture, of an elliptical form, enters the vestibule. The third is the aperture of the aqueeductus cochle~, leading to a minute funnel-shaped canal, which opens on the basilar surface of the petrous bone and transmits a small vein, and also forms a communication between the subarachnoidean space of the skull and the perilymph contained in the scala tympani.


The lamina spiralis ossea is a bony shelf or ledge which projects outward from
the modiolus into the interior of the spiral canal, and, like the canal, takes two and three-quarter turns round the modiolus. It reaches about half-way toward the outer wall of the spiral tube, and partially di "ides its cavity into two passages or scalee, of which the upper is named the scala vestibuli, while the lower is termed the scala tlj1nlJani. Near the summi t of the cochlea the lamina terminates in a hook-shaped •process, the hamulus, which assists to form the boundary of a small opening, the helicotrema, by which the two scalse communicate with each other. From the canalis spiralis modioli numerous foramina pass outward through the osseous spiral lamina as far as its outer or free edge. In the lower part of the first

THE SACRAL PLEXUS.

The femoral cutaneous branches (descending) are numerous filaments, derived from both sides of the nerves, which are distributed to the back, inner, and outer sides of the thigh, to the skin covering the popliteal space, and to the upper part
of the leg.
The Perforating Cutaneous Nerve usually arises from the second and third sacral
nerves, and is of small size. It is continued backward through the great sacro¬sciatic ligament, and, winding round the lower border of the Gluteus maximus, supplies the integument covering the inner and lower part of that muscle.
The Pudic Nerve is the direct continuation of the lower cord of the sacral plexus, and derives its fibres from the third and fourth sacral nerves,and frequently from the second also. It leaves the pelvis through the great sacro-sciatic foramen, below the Pyriformis. It then crosses the spine of the ischium, and re-enters the pelvis through the lesser sacro-sciatic foramen. It accompanies the pudic vessels upward and forward along the outer wall of the ischio-rectal fossa, being contained in a sheath of the obturator fascia, termed Alcoclc's canal, and divides into two terminal branches. the perineal nerve and the dorsal nerve of the penis or clitoris. Before its division it gi ves off the inferior hemorrhoidal nerve.
The inferior hemorrhoidal nerve is occnsionally derived separately from the sacral plexus. It passes across the iscbio-rectal fossa, with its accompanying vessels, toward the lower end of the rectum, and is distributed to the Sphincter ani externus and to the integument round the anus. Branches of this nerve com¬municate with the inferior pudendal and superficial perineal nerves at the fore part
of the perineum.
The perineal nerve, the inferior and larger of the two terminal branches of the
pudic, is situated below the pudic artery. It accompanies the superficial perineal artery in the perineum, dividing into cutaneous and muscular branches.

THE DORSAL NERVES.

They pass forward in the intercostal spaces with the intercostal vessels, being situated below them. At the back of the chest they lie between the pleura and the External intercostal muscle, but are soon placed between the two planes of Intercostal muscles as far as the middle of the rib. They then enter the substance of the Internal intercostal muscles, and, running amidst their fibres as far as the costal cartilages, they gain the inner surface of the muscles and lie between them and the pleura. Near the sternum. they cross in front of the internal mam¬mary artery and Triangularis sterni muscle. pierce the Internal intercostal muscles, the anterior intercostal membrane. and Pectoralis major muscle, and supply the integument of the front of the chest and over the mammary gland, forming the anterior cutaneous nerves of the thorax; the branch from the second nerve is joined with the eupraclavicular nerves of the cervical plexus.

Branches.-Numerous slender muscular filaments supply the Intercostals, the Infracostales, the Levatores costarum, Serratus posticus superior, and Triangularis sterni muscles. Some of these branches, at the front of the chest, cross the costal cartilages from one to another intercostal space.

Lateral Cutaneous .cVerves.-These are derived from the intercostal nerves, midway between the vertebras and sternum; they pierce the External intercostal and Serratus magnus muscles, and divide into two branches, anterior and posterior.

The anterior branches are reflected forward to the side and the fore part of the chest, supplying the integument of the chest and mamma; those of the fifth and sixth nerves supply the upper digitations of the External oblique.

The posterior branches are reflected backward to supply the integument over the scapula and over the Latissimus dorsi.

The lateral cutaneous branch of the second intercostal nerve is of large size, and does not divide, like the other nerves, into an anterior and posterior branch. It is named, from its origin and distribution, the intercosto-humeral nerve (Fig. 413). It pierces the External intercostal muscle, crosses the axilla to the inner side of the arm, and joins with a filament from the nerve of Wrisberg. It then pierces the fascia, and supplies the skin of the upper half of the inner and back part of the arm, communicating with the internal cutaneous branch of the musculo-spiral nerve. The size of this nerve is in inverse proportion to the size of the other cutaneous nerves, especially the nerve of W risberg. A second intercosto-humeral nerve is frequently given off

THE SPHENOID BONE.

The Lesser Wings (proces8es of Ingrassias) are two thin, triangular plates of bone which arise from the upper and lateral parts of the body of the sphenoid, and, projecting transversely outward, terminate in a sharp point (Fig. 37). The superior surface of each is smooth, flat, broader internally than externally, and supports part of the frontal lobe of the brain. The inferior surface forms the¬back part of the roof of the orbit and the upper boundary of the sphenoidal fissure or foramen lacerum anterius. This fissure is of a triangular form, and leads from the cavity of the cr&nium into the orbit; it is bounded internally by the body of the sphenoid-above, by the lesser wing; below, by the internal margin of the orbital surface of the great wing-and is converted into a foramen by the articu¬lation of this bone with the frontal. It transmits the third, the fourth, the three branches of the ophthalmic division of the fifth, the sixth nerve, some filaments from the cavernous plexus of the sympathetic, the orbital branch of the middle meningeal artery, a recurrent branch from the lachrymal artery to the dura mater, and the ophthalmic vein. The anterior border of the lesser wing is ser¬rated for articulation with the frontal bone; the posterior, smooth and rounded, is received into the fissure of Sylvius of the brain. The inner extremity of this border forms the anterior clinoid process.• The lesser wing is connected to the side of the body by two roots, the upper thin and flat, the lower thicker, obliquely directed, and presenting on its outer side, near its junction with the body, a smail tubercle, for the attachment of the common tendon of origin of three of the muscles of the eye. Between the two roots is the optic foramen, for the transmission of

The Pterygoid Processes (rrripu;, a wing; 0100" likeness), one on each side, descend perpendicularly from the point where the body and greater wing unite (Fig. 39). Each process consists of an external and an internal plate, which are joined together by their anterior borders above, but are separated below, leaving an angular cleft, the pterygoid notch, in which the pterygoid process or tuberosity of the palate bone is received. 'I'he two plates diverge from each other from their line of connection in front, so as to form a V-shaped fossa, the pterygoid f08sa. The external pterygoid plate is broad and thin, turned a little outward, and, by its outer surface, forms part of the inner wall of the zygomatic fossa, giving attachment to the External pterygoid; its inner surface forms part 

 

THE SPINE IN GENERAL.

The lateral surfaces are separated from the posterior by the articular processes in the cervical and lumbar regions, and by the transverse processes in the dorsal. These surfaces present in front the sides of the bodies of the vertebral, marked in the dorsal region by the facets for articulation with the heads of the .ribs. More posteriorly are the intervertebral foramina, formed by the juxtaposition of the intervertebral notches, oval in shape, smallest in the cervical and upper part of the dorsal regions, and gradually increasing in size to the last lumbar.

 They arc situated between the transverse processes in the neck, and in front of them in' the back and loins, and transmit the spinal nerves.
The base of that portion of the vertebral column formed by the twenty-four movable vertebral is formed by the under surface of the body of the fifth lumbar vertebra; and the summit by the upper surface of the atlas.
The vertebral or spinal ca.nal follows the different curves of the spine; it is largest in those regions in which the spine enjoys the greatest freedom of move¬ment, as in the neck and loins, where it is wide and triangular; and narrow and rounded in the back, where motion is more limited.

THE •PERICARDIUM.

The serOU8 layer invests the heart, and is then reflected on the inner surface of the pericardium. It consists, therefore, of a visceral and parietal portion. The former invests the surface of the heart, and the commencement of the great vessels,
. to the extent of an inch and a half from their origin; from these it is reflected upon the inner surface of the fibrous layer, lining, below, the upper surface of the central tendon of the Diaphragm. The serous membrane encloses the aorta and pulmonary artery in a single tube, so that a passage, termed the transverse sinus of the pericardium, exists between these vessels in front and the auricles behind.

The membrane only partially covers the superior vena cava and the four pulmonary veins, and scarcely covers the inferior cava, as this vessel enters the heart almost directly after it has passed through the Diaphragm. Its inner surface is smooth and glistening, and secretes a serous fluid, which serves to facilitate the movements
of the heart.
Arteries of the Pericardium.-These are derived from the internal mammary
and its musculo-phrenic branch, and from the descending thoracic aorta.
Nerves of the Perieardium.-These are branches from the vagus, the phrenic,
and the sympathetic.

THE HYOID BONE.

I'he pos The lateral surfaces after middle life are joined to the greater cornua. In early life they are connected to the cornua by cartilaginous surfaces, and held together by liga¬
ments, and occasionally a synovial membrane is found between them.

The Greater Cornua (thyro-hyal) project backward from the lateral surfaces of the body; they are flattened from above downward, diminish in size from before, backward, and terminate posteriorly in a tubercle for the attachment of the lateral thyro-hyoid ligament. The outer surface gives attachment to the Hyo-glossus, their upper border to the Middle constrictor of the pharynx, their lower border to
part of the Thyro-hyoid muscle.

The Lesser Cornua (cerato-ltyals) are two small, conical-shaped eminences attached by their bases to the angles of junction between the body and greater cornua, and giving attachment by their apices to the stylo-hyoid ligaments.' The smaller cornua are connected to the body of the bone by a distinct diar¬throdial joint, which usually persists throughout life, but occasionally becomes
ankylosed.

THE PLEURAE.

Tracheotomy may be performed either above or below the isthmus of the thyroid body, or ".
this structure may be divided and the trachea opened behind it.
The isthmus of the thyroid gland usually crosses the second and third rings of the trachea;
along its upper border is frequently to be found a large transverse communicating branch between the superior. thyroid veins; and the isthmus itself is covered by a venous plexus formed between the thyroid veins of the opposite sides. Theoretically, therefore, it is advisable to avoid dividing
this structure in opening the trachea.
Above the isthmus the trachea is comparatively superficial, being covered by the skin, super-
ficial fascia, deep fascia, St.erno-hyoid and Sterno-thyroid muscles, and a second layer of the deep fascia, which, attached above to the lower border of the hyoid bone, descends beneath the muscles to the thyroid body, where it divides into two layers and encloses the isthmus.
Below the isthmus the trachea lies much more deeply, and is covered by the Sterno-hyoid and the Sterno"thyroid muscles and a quantity of loose areolar tissue in which is a plexus of veins, some of them of large size; they converge to two trunks, the inferior thyroid veins, which descend on either side of the median line on the front of the trachea and open into the innomi-nate veins. In the infant the thymus gland ascends a variable distance along the front of the trachea, and opposite the episternal notch the windpipe is crossed by the left innominate vein. Occasionally also, in young subjects, the innominate artery crosses the tube obliquely above the level of the sternum. The thyroidea ima artery, when that vessel exists, passes from below up"
ward along the front of the trachea.
From these observations it must be evident that the trachea can be more readily opened
above than below the isthmus of the thyroid body.
Tracheotomy above the isthmus is performed thus: the patient should, if possible, be laid
on his back on a table in a good light. A pillow is to be placed under the shoulders and the head thrown back and steadied by an assistant. The surgeon standing on the right side of his
patient makes an incision from an inch and a half to two inches in length in the median line of the neck from the top of the cricoid cartilage. The incision must be made exactly in the middle line, so as to avoid the anterior jugular veins, and after the superficial structures have been divided the interval between the Sterno-hyoid muscles must be found, the raphe divided, and the muscles drawn apart. The lower border of the cricoid cartilage must now be felt for, and the upper part of the trachea exposed from this point downward in the middle line. Bose has recommended that the layer of fascia in front of the trachea should be divided transversely at the level of the lower border of the cricoid cartilage, and, having been seized with a pair of forceps pressed downward with the handle of the scalpel. By this means the isthmus of the thyroid gland is d<,pressed, and is saved from all danger of being wounded, and the trachea cleanly exposed. The trachea is now transfixed with a sharp book and drawn forward in order to steady It, and is then opened by inserting the knife into it and dividing the two or three upper rings from below upward. If the trachea is to be opened below the isthmus, the incision must be made from a little below the cricoid cartilage to the top of the sternum.

THE THYMUS GLAND.

Vessels and Nerves.-The arteries supplying the thyroid are the superior and inferior thyroid, and sometimes an additional branch (thyroidea media or ima) from the innominate artery or the arch of the aorta, which ascends upon the front of the trachea. The arteries are remarkable for their large size and frequent anastomoses. The veins form a plexus on the surface of the gland and on the front of the trachea, from which arise the superior, middle, and inferior thyroid veins, the two former terminating in the internal jugular, the latter in the innom-inate vein. The lymphatics are numerous, of large size, and terminate in the thoracic and right lymphatic. ducts. The nerves are derived from the middle and inferior cervical ganglia of the sympathetic. 

Surgical Anatomy.-The thyroid gland is subject to enlargement, which is called goitre. 

This may be due to hypertrophy of any of the constituents of the gland. The simplest (parenchymatous goitre) is due to an enlargement of the follicles. The fibroid is due to increase of the interstitial connective tissue. The cystic is that form in which one or more large cysts are formed from dilatation and possibly coalescence of adjacent follicles. The pulsating goitre is where the vascular changes predominate over the parenchymatous, and the vessels of the' gland are especially enlarged. Finally, there is exophthalmic goitre (Graves's disease), where there is great vascularity and often pulsation, accompanied by exophthalmos, palpitation, and 

rapid pulse. 

. For the relief of these growths various operations have been resorted to, such as injection 

of tincture of iodine or perchloride of iron, especially applicable to the cystic form of the disease, ligature of the thyroid arteries, excision of the isthmus, and extirpation of the whole or a part of the gland. This latter operation is one of difficulty, and when the entire gland has been removed the operation has been followed by a condition resembling myxredema. In removing the organ great care must, be taken to avoid tearing the capsule, as if this happens the gland-tissue bleeds profusely. The thyroid arteries should be Jig-atured before an attempt is made to remove the mass, and in ligaturing the inferior thyroids the position of the recurrent laryngeal nerve must be borne in mind, so as not to include it in the ligature. A large number of cases of what were formerly supposed to be goitre are now known to be cases of adenomatous enlarge-ment, where an adenoma, starting in one part of the gland, gradually spreads and involves the 

whole organ.