From the right division of the plexus the branches proceed before and behind the right pulmonary artery. Those which pass in front descend upon the trunk of the pulmonary artery to the left coronary artery, and help to form the anterior coronary plexus; those which pass behind the right pulmonary artery are distributed to the right auricle; a third set of filaments, proceeding from the right division of the deep cardiac plexus, follow the course of the right pulmonary artery to the anterior pulmonary plexus.

From the left division of the plexus branches proceed beneath the arch of the aorta immediately to the right of the ligament of the ductus arteriosus to join the superficial cardiac plexus; others pass outwards with the pulmonary artery to the pulmonary plexus; a few descend to the left auricle; but the chief bulk pass on to the right coronary artery and form the posterior coronary plexus.

The Anterior coronary plexus proceeds from the superficial cardiac plexus, and receives other filaments from the deep cardiac plexus. It is distributed with the branches of the coronary artery on the anterior aspect of the heart.

The Posterior coronary plexus proceeds from the deep cardiac plexus and principally from its left division. It follows the course of the arteries distributed to the posterior aspect of the heart.

THORACIC PORTION OF THE SYMPATHETIC NERVE.

[FIG. 286.

THE GANGLIA OF THE SYMPATHETIC IN THE CHEST; (the ganglia are represented larger than natural); from part of a plate in Mr. Swan's work. a.

Aorta. b. First rib. c. Eleventh rib. 1. First thoracic ganglion. 2. Last thoracic ganglion. 3. The great splanchnic nerve. 4. The lesser

splanchnic nerve. 5. Third or renal splanchnic nerve. 6. Part of the brachial plexus.]

The thoracic portion of the sympathetic nerve is the trunk of the sympathetic in its course through the cavity of the thorax. It lies by the side of the vertebral column on the heads of the ribs and intercostal spaces; but at its lowest part comes into relation with the sides of the bodies of the last two dorsal vertebræ.

The Thoracic ganglia are twelve in number at each side. They are flattened and triangular, or irregular in form, and present the peculiar reddish-gray color and pearly lustre of sympathetic ganglia in general; they rest against the heads of the ribs, and are covered by the pleura costalis. The first two ganglia and the last are usually the largest; the latter being situated on the side of the body of the last dorsal vertebra.

Their branches are branches of communication and branches of distribution. Some ascending filaments from the first ganglion assist in the formation of the vertebral plexus.

The external or communicating branches, usually two in number for each ganglion, communicate with the intercostal nerves.

The internal or viscerul branches proceeding from the five or six upper ganglia, are of small size, and distributed to the aorta, oesophagus, vertebral column, and lungs. The branches to the lungs proceed from the third and fourth ganglia, and go to join the posterior pulmonary plexus. The visceral branches of the six lower ganglia unite to form the three splanchnic

nerves.

The Great splanchnic nerve proceeds from the sixth dorsal ganglion, and receiving the

branches of the seventh, eighth, ninth, and tenth, passes downwards along the front of the vertebral column, and, piercing the crus of the diaphragm, terminates in the semilunar ganglion.

The Lesser splanchnic nerve is formed by filaments which issue from the tenth and eleventh ganglia; it pierces the crus of the diaphragm, and joins the the solar plexus near the middle line.

The Third or renal splanchnic nerve proceeds from the last thoracic ganglion, and, piercing the diaphragm, terminates in the renal plexus. When absent, the place of this nerve is supplied by the lesser splanchnic.

The Semilunar ganglion is a large, irregular, gangliform body, pierced by numerous openings, and appearing like the aggregation of a number of smaller ganglia, having spaces between them. It is situated by the side of the coeliac axis and root of the superior mesenteric artery, and extends outwards to the supra-renal capsule. The ganglia communicate both above and below the coeliac axis and form a gangliform circle, from which branches pass off in all directions, like rays from a centre. Hence the entire circle has been named

the solar plexus.

The Solar or epigastric plexus receives the great and lesser splanchnic nerves; the termination of the right pneumogastric nerve; some filaments from the right phrenic nerve; and sometimes one or two from the left. It sends forth numerous filaments which accompany, under the name of plexuses, all the branches given off by the abdominal aorta.

solar plexus, the

Phrenic, or diaphragmatic plexuses,

Gastric plexus,

Hepatic plexus,

Splenic plexus,

Supra-renal plexuses,

Thus we have, derived from the

In connexion with the phrenic plexus of the right side, there is described a small ganglion diaphragmaticum, which is situated near the supra-renal capsule. In this ganglion branches of the right phrenic nerve communicate with those of the sympathetic.

The Supra-renal plexuses are remarkable for their large size, and for a ganglion, which has received the name of ganglion supra-renale.

The Renal plexuses are large, and receive the third splanchnic nerve.

The Superior mesenteric plexus has several small ganglia at the root of the artery; and its nerves, which are whiter than those of the other plexuses, form a kind of nervous sheath to the artery and its branches.

The Aortic plexus is a continuation of the solar plexus downwards on the aorta, for the supply of the inferior branches of that trunk; it receives also branches from the renal plexuses and lumbar ganglia. It is the source of origin of the inferior mesenteric plexus and part of the spermatic plexus, and terminates below in the hypogastric plexus. It likewise distributes branches on the inferior vena cava.

The Spermatic plexus is derived from the renal plexus, but receives filaments from the aortic plexus.

The Inferior mesenteric plexus is derived chiefly from the aortic plexus.

LUMBAR PORTION OF THE SYMPATHETIC NERVE.

The lumbar portion of the trunk of the sympathetic is situated on the vertebral column, close to the anterior border of the psoas magnus muscle. It is continuous above under the edge of the diaphragm, with the thoracic portion of the nerve, and below it descends upon the sacrum, in front of the anterior

sacral foramina, to the coccyx. It presents four small ganglia and an intermediate cord.

The Lumbar ganglia, four in number at each side, of a pearly-gray color and fusiform shape, are situated on the anterior part of the bodies of the lumbar vertebræ.

The branches of the lumbar ganglia are branches of communication and branches of distribution.

The external or communicating branches, two or three in number from each ganglion, and longer than in the other regions, communicate with the lumbar

nerves.

The internal or visceral branches consist of two sets; the upper pass inwards in front of the abdominal aorta, and join the aortic plexus; the lower cross the common iliac arteries, and unite over the promontory of the sacrum, to form the hypogastric plexus.

The Hypogastric plexus is formed by the termination of the aortic plexus, and by the union of branches from the lower lumbar ganglia. It is situated over the promontory of the sacrum, between the two common iliac arteries, and bifurcates inferiorly into two lateral portions, inferior hypogastric plexuses, which communicate with branches from the third and fourth sacral nerves. It distributes branches to the viscera of the pelvis, and sends filaments which accompany the branches of the internal iliac artery.

SACRAL PORTION OF THE SYMPATHETIC NERVE.

The Sacral ganglia are four or five in number at each side. They are situated on the sacrum, close to the anterior sacral foramina, and resemble the lumbar ganglia in form and mode of connexion, although much smaller in size.

The external or communicating branches are two from each ganglion, which pass outwards to communicate with the anterior sacral nerves and with the coccygeal nerve.

The last pair situated on the This ganglion It gives off a

The internal or visceral branches communicate very freely with the inferior hypogastric plexuses, and are distributed to the pelvic viscera. of sacral ganglia give off branches which join a small ganglion, first bone of the coccyx, called the ganglion impar, or azygos. serves to connect the extremities of the two sympathetic nerves. few small branches to the coccyx and rectum, and communicates with the coccygeal nerve.

CHAPTER X.

ORGANS OF SENSE.

THE organs of sense, the instruments by which the animal frame is brought into relation with surrounding nature, are five in number. Four of these organs are situated within the head: viz., the apparatus of smell, sight, hearing, and taste; the remaining organ, that of touch, is resident in the skin, and distributed over the surface of the body.

ORGAN OF SMELL.

The organ of smell consists essentially of two parts: one external, the nose; the other internal, the nasal fossa.

NOSE.

The nose is the triangular pyramid which projects from the centre of the face, immediately above the upper lip. Superiorly it is connected with the forehead by means of a narrow bridge; inferiorly, it presents two openings, the nostrils,' [anterior nares,] which overhang the mouth, and are so constructed that the odor of all substances must be received by the nose before they can be introduced within the lips. The septum between the openings of the nostrils is called the columna. Their entrance is guarded by a number of stiff hairs (vibrissæ) which project across the openings, and act as a filter in preventing the introduction of foreign substances, such as dust or insects, with the current of air intended for respiration.

The anatomical elements of which the nose is composed, are, 1. Integument. 2. Muscles. 3. Bones. 4. Fibro-cartilages. 5. Mucous membrane. 6. Vessels and nerves.

1. The Integument forming the tip (lobulus) and wings (ale) of the nose is extremely thick and dense, so as to be with difficulty separated from the fibrocartilage. It is furnished with an abundance of sebiparous glands, which, by their oily secretion, protect the extremity of the nose under alternations of temperature. The sebaceous matter of these glands becomes of a dark color near the surface, from altered secretion, and also from attraction of the carbonaceous matter floating in the atmosphere; hence the spotted appearance which the tip of the nose presents in large cities. When the integument is firmly compressed, the inspissated sebaceous secretion is squeezed out, and, taking the cylindrical form of the excretory ducts of the glands, has the appearance of small white maggots (grubs; comedones) with black heads.

2. The Muscles are brought into view by reflecting the integument; they are the pyramidalis nasi, compressor naris, dilatator naris, levator labii superioris alæque nasi, and depressor alæ nasi. They have been already described with the muscles of the face.

3. The Bones of the nose are, the nasal, and nasal processes of the superior maxillary.

4. The Fibro-cartilages give form and stability to the nose, providing, at the same time, by their elasticity against injuries. They are five in number, namely, the

Fibro-cartilage of the septum,
Two lateral fibro-cartilages,
Two alar fibro-cartilages.

The Fibro-cartilage of the septum, somewhat triangular in form, divides the nose into its two nostrils. It is connected above with the nasal bones and lateral fibro-cartilages; behind, with the ethmoidal septum and vomer; and below, with the palate processes of the superior maxillary bones. The alar fibro-cartilages and columna move freely on the fibro-cartilage of the septum, being but loosely connected with it by perichondrium.

The Lateral fibro-cartilages are also triangular; they are connected, in front, with the fibro-cartilage of the septum ; above, with the nasal bones; behind, with the nasal processes of the superior maxillary bones; and below, with the alar fibro-cartilages.

Alar fibro-cartilages.-Each of these cartilages is curved so as to correspond with the walls of the nostril, to which it forms a kind of rim. The inner portion is loosely connected with the same part of the opposite cartilage, to form the columna. It is expanded and thickened at the point of the nose, to consti

[The word nostril is employed in a somewhat more extended sense than "aperture," and would seem properly to refer to each lateral cavity of the nose, forming a vestibule to its appropriate nasal fossa.]

tute the lobe [lobulus]; and on the side makes a curve corresponding with that of the ala. This curve is prolonged backwards and downwards in the direction of the posterior border of the ala by three or four small fibro-cartilaginous plates (sesamoid cartilages, cartilagines minores), which are appendages of the alar fibro-cartilage.

Fig. 287.

Fig. 288.

3

THE FIBRO-CARTILAGES OF THE NOSE. 1. One of the nasal bones. 2. Cartilage of the septum. 3. Lateral cartilage. 4. Alar cartilage. 5. Central portions of the alar cartilages which constitute the columna. 6. Cartilagines minores or sesamoid cartilages. 7. The nostril.

THE FIBRO-CARTILAGES AND BONES of the nose, viewed from the side; after Arnold. a. Nasal bone. b. Nasal process of the superior maxillary bone. 4. Cartilage of the septum. 1. Lateral cartilage. 2. Alar cartilage. 2. Inner portion of the alar cartilage. 3. Sesamoid cartilages. 5. Areolar tissue of the ala nasi. 6. Aperture of the nostril.

The whole of these fibro-cartilages are connected with each other, and to the bones, by perichondrium, which, from its membranous structure, permits of the freedom of motion existing between them.

5. The Mucous membrane lining the interior of the nose, is continuous with the skin externally, and with the pituitary membrane of the nasal fosse within. Around the entrance of the nostrils it is provided with the vibrissæ.

6. Vessels and Nerves. - The Arteries of the nose are the lateralis nasi from the facial, and the nasalis septi from the superior coronary.

Its Nerves are, the facial, infraorbital, and nasal branch of the ophthalmic.

NASAL FOSSE.

To obtain a good view of the nasal fossa, the face must be divided through the nose by a vertical incision, a little to one side of the middle line.

The Nasal fossa [nares internæ] are two irregular, compressed cavities, extending backwards from the nose to the pharynx. They are [each] bounded superiorly by the lateral cartilage of the nose, and by the nasal, ethmoid, and sphenoid bone; inferiorly, by the hard palate; and, in the middle line, they are separated by a bony and fibro-cartilaginous septum. A plan of the boundaries of the nasal fosse will be found at page 91.

On the outer wall of each fossa, in the dried skull, are three projecting processes, termed spongy bones. The two superior belong to the ethmoid, the inferior is a separate bone. In the fresh fossa these are covered with mucous membrane, and serve to increase the surface of that membrane by their promiuence and convoluted form. The space intervening between the superior and