Part 39

41. The tarsal muscles (p. 215). The overlying ligaments must be removed in order to expose the scaphocuneiform.

IX. THE DIAPHRAGM AND THE MUSCLES ON THE VENTRAL SIDE OF THE VERTEBRAL COLUMN IN THE LUMBAR AND PELVIC REGIONS.

Remove the ventral and lateral walls of the thorax completely, as far back as the diaphragm,--leaving only a ring attached to the margin of the diaphragm. Remove the abdominal walls in the same way, as far back as the pubis, leaving the diaphragm in position. Remove the thoracic viscera (the heart and lungs may be preserved for future study). Remove also the abdominal viscera as far back as the beginning of the pelvis, cutting the large intestine where it passes into the pelvis. The dorsal wall of the abdominal cavity should be cleared of fat, blood-vessels, etc., without injury to the crura of the diaphragm.

1. The diaphragm (p. 151, and Fig. 74). Study by transmitted light, to see the tendons, etc.

2. The psoas minor (p. 139, and Fig. 162, 9, p. 398). Find its tendon and separate it from the iliopsoas (Fig. 162, 8) as far craniad as this can be done without tearing the fibres.

3. The iliopsoas (p. 193, and Fig. 162, 8). Find both portions; isolate them as far as it can be done.

4. The quadratus lumborum (p. 139). Free the lateral edge of the iliopsoas from the abdominal wall and turn the whole muscle mediad as far as possible. The bundles of the quadratus lumborum will be found beneath it, against the transverse processes of the lumbar vertebræ.

With a heavy cartilage-knife separate the two innominate bones along the pelvic symphysis. This is easily done if the knife is inserted exactly into the line of junction of the two bones. Divaricate the edges some distance, so as to make a ventral opening into the pelvic cavity. If necessary, part of the innominate bone of one side may be removed to make the opening larger.

Find the thin sheet of fibres forming the levator ani muscle (Fig. 162, 11) at the side of the rectum, attached to the edge of the symphysis. Carefully free the rectum and urogenital organs from this and remove them as far as the anus, leaving the levator ani intact.

5. The iliocaudalis (p. 137, and Fig. 162, 11′).

6. The levator ani (p. 269, and Fig. 162, 11).

Remove with great care the levator ani and iliocaudalis of one side, by cutting first the attachment to the symphysis and the ilium, turning the muscle mediad, then cutting the attachment to the tail. There are thus exposed on the lateral wall of the thorax the medial surface of the obturator internus, craniad of it the pyriformis, caudad of it the quadratus femoris. Dorsad of these is the abductor caudæ internus.

7. The abductor caudæ internus (p. 137).

On the ventral surface of the tail are exposed the following:

8. The flexor caudæ longus (p. 138, and Fig. 162, 12).

9. The flexor caudæ brevis (p. 138, and Fig. 162, 13).

X. MUSCLES OF THE TAIL (p. 136).

By removing the skin of the tail, all the muscles of the tail are now easily seen.

1, 2, 3, 4, 5--see 5, 6, 7, 8, 9, above (IX).

6. The abductor caudæ externus (p. 137, and Fig. 113, _b_; Fig. 70, _g_).

7. The extensor caudæ lateralis (p. 137, and Fig. 70, _f_).

8. The extensor caudæ medialis (p. 136, and Fig. 70, _e_).

THE VISCERA.

Kill the specimen with chloroform and inject with the five per cent. formalin, or the mixture of formalin and glycerine, as for the muscles. (It is an advantage if the preliminary examination of the viscera can be done in a perfectly fresh, uninjected specimen; such a specimen can be kept but a day or two, however. After one day’s examination the skin may be removed and the specimen placed in two per cent. formalin; it will usually be fairly well preserved by this, though the formalin is too strong to make the later dissection pleasant. The specimen cannot be preserved in this manner unless the skin is removed, and a sufficient quantity of formalin used.)

PRELIMINARY EXAMINATION OF THE VISCERA.

(In this preliminary examination the descriptions in the text need not be read, except when this is specially directed.)

Wet the hair along a line from the symphysis of the jaw to the pubis.

## Part it and make a longitudinal incision through the skin along the

line. Make a transverse incision of the skin five centimeters caudad of the xiphoid process and reflect the flaps. Incise the body wall from the last rib to the pelvis along the same line as above and also transversely. Reflect the flaps without injuring the ligaments of the bladder. Make an incision through the pectoral muscles between the first rib and the ventral attachment of the diaphragm and about one centimeter from the median line. Make a second incision of the muscles from the cranial end of the first incision along the angles of the ribs to near the dorsolateral attachment of the diaphragm. Cut the ribs and thoracic wall along these incisions with strong scissors; connect the two incisions at their caudal ends, and remove the lateral thoracic wall thus circumscribed. Note the thoracic and abdominal cavities, separated by the diaphragm.

Note the following viscera in their fresh condition:

A. In the abdominal cavity (without injuring anything)

1. The liver, dark red and lobed, in the cranial part of the cavity, lying against the diaphragm.

2. The gall-bladder partly imbedded in the right median lobe.

3. Displacing the liver craniad, the stomach is seen dorsad of its left lobe. It may extend dorsad of the right lobe, its size depending on the degree of distension.

4. The duodenum or first part of the small intestine leaves the stomach at its right side craniad and makes a U bend, the head of which is directed caudad; it then turns toward the middle line dorsad of the remaining part of the small intestine.

5. The great omentum is a thin fold of peritoneum with many bands of fat. It passes like a curtain from the great curvature of the stomach ventrad of the coils of the small intestine (ileum). It is tucked beneath the mass of coils at the sides and caudally, and folds of it extend between the individual coils. Turn it craniad and note--

6. The numerous coils of the third part of the small intestine or ileum. Turn these to one side and note--

7. The connection of the ileum with the duodenum across the middle line. An indefinite part of the intestine between the ileum and duodenum is called the jejunum, because in man it is found empty after death.

8. The passage of the ileum into the side of the large intestine which begins on the right side just caudad of the loops of the duodenum. The first part of the large intestine is the colon. It may be traced first toward the head (ascending colon), then sinistro-caudad (transverse colon) and then caudad (descending colon). The descending colon returns to the middle line and the large intestine then continues to the anus as the rectum.

The blind pouch of the colon which lies caudad of the opening of the ileum is the cæcum.

9. Turn the duodenum toward the left and note the pancreas, a light red, elongated organ which stretches along the greater curvature of the stomach and thence between the two lines of the duodenal U to its bottom.

10. The spleen, parallel to the gastric portion of the pancreas. It is deep red (darker than the pancreas and not so brown as the liver) and is held against the great curvature of the stomach by a part of the great omentum.

11. The kidneys, close against the dorsal body wall and in contact with the caudal part of the liver.

12. The bladder, in the median line at the caudal end of the cavity, held in place by the suspensory ligament, which passes to the midventral line, and by the lateral ligaments.

13. The mesenteric glands, large grayish-red glands one to four centimeters long, more numerous in the mesocolon.

14. In the female, lying against the ventral surface of the rectum, the uterus. It divides into two horns which diverge. Near the end of each horn the ovary.

15. The peritoneum. Study and understand the description of it (p. 218). Dissect some of it free from the body wall. (Trace the folds by aid of a diagram and model.)

B. In the thoracic cavity:

1. The lungs. Each is divided into lobes, three on the left, four on the right. The caudal right lobe pushes the mediastium toward the left and thus lies in a pocket dorsocaudad of the heart and dorsad of the vena cava inferior.

2. The pleuræ. Each pleura is a membrane like the peritoneum. It covers the diaphragm and the thoracic walls and is reflected onto the lungs. Hence it is divided into costal and pulmonary portions. Read the description (p. 217) and trace their connection. Each pleura forms a closed sac.

3. The mediastinal septum or median vertical portion formed by the apposition of the medial walls of the two pleural sacs. It divides the thorax into halves.

4. In the mediastinum or space between the halves of the mediastinal septum are seen--

_a._ Ventrally (i.e., in the anterior mediastinum), blood-vessels and fat, and craniad the pink thymus gland. Read the description of the thymus (p. 254, and Fig. 107).

_b._ Dorsally (i.e., in the posterior mediastinum) the trachea (best seen craniad), the œsophagus (best seen caudad), and the aorta.

_c._ In the middle (reckoning in a dorsoventral line) (i.e., in the middle mediastinum) the heart, with the inferior vena cava approaching it from the rear. Prick into the mediastinum and inflate it. Remove the thoracic wall opposite the one already removed, so as to stretch the mediastinum and show it more clearly. Expose the trachea beneath the caudal end of the sternomastoidei. Note the thyroid gland (Fig. 96, 6, p. 229). Insert a blowpipe without injury to the thyroid, and inflate the lungs. Cut the sternum at its caudal end and turn it craniad, cutting the mediastinal septum and noting its double character.

Dissect the mediastinal septum from the thymus so as to expose this organ.

_d._ The pericardium, a relatively thick-walled sac, within which the heart lies. The pericardium is covered by the mediastinal septum on each side, but not dorsally and ventrally. Dissect the mediastinal septum from the pericardium. Prick and inflate the pericardium. Open it and expose the heart.

DISSECTION OF THE ALIMENTARY CANAL.

Study and verify the descriptions of the organs as they are dissected.

I. Salivary glands (p. 223).

1. Keep the mouth open by a cork between the teeth. Find the papillæ upon which open the sublingual and submaxillary ducts (pp. 223 and 224); remove the mucosa and enlarge the opening and insert a black bristle into either duct. Trace the duct by the bristle as far as possible on the floor of the mouth.

2. Find the white ridge formed on the cheek by the parotid duct (p. 223). It is opposite the molar tooth, and at its cranial end the opening of the duct is seen. Enlarge the opening and insert a black bristle as far as possible.

3. Remove the skin and the skin-muscles from the side of the face, beginning at the caudal end and working craniad. At the cranial border of the carotid on the ventral side look carefully for the parotid duct with the bristle in it. The duct is then easily traced by the removal of the skin and muscles. Study the parotid gland (Fig. 131, 10, p. 322).

4. Remove the facial vein (Fig. 131, _b_ and _c_) and lymphatic gland (Fig. 131, 12) covering the submaxillary gland (Fig. 131, 11) and clean its outer surface. Raise it and find the submaxillary duct leaving its inner surface. Reflect the digastric and mylohyoid muscles and trace the duct to the oral mucosa. The remainder of its course is shown by the bristle on the inside of the mouth.

5. The sublingual gland is uncovered in dissecting the submaxillary. Its duct is seen by the side of the submaxillary. It may be pricked near the gland and a bristle passed to its opening.

6. The infraorbital gland. Expose it by removal of the zygomatic arch and masseter muscle. Find its duct by dissecting apart the lobules at its ventral end. Prick the duct and insert a bristle to find its inner opening.

7. The molar gland. Find it by raising the orbicularis oris of the lower lip. By raising its ventral border and dissecting between it and the mucosa the ducts may be found and perhaps pricked and bristles inserted.

II. The mouth-cavity. Study the general description (p. 221); the lips and the cheek. Then remove the masseter muscle and the caudal part of the zygoma. Cut through the mandible between the first premolar and the canine tooth. Then disarticulate the mandible, cut the cheek and also the mylohyoid muscle and oral mucosa parallel to the medial border of the mandible, and remove the mandible with the parts thus left attached to it. The organs in the mouth-cavity are thus left exposed and should be studied. To demonstrate the incisive ducts (p. 222) pass a bristle into them.

The teeth (p. 224). These should be studied on a skull in which the roots of the teeth have been laid bare by means of the bone-forceps, as in Figs. 93 and 94.

The tongue (p. 226, and Fig. 95). Study its dorsal surface, the papillæ, etc. Then dissect its _muscles_ (p. 228) from the ventral side. The stylohyoid, digastric, and mylohyoid muscles must be removed. Then dissect (_a_) the styloglossus (Fig. 96, _e_), (_b_) the genioglossus (Fig. 96, _f_), (_c_) the hyoglossus (Fig. 96, _h_). Make a transverse section of the tongue to see the intrinsic muscle-fibres.

III. The thyroid gland (p. 254, and Fig. 96, 6). Clean the sternomastoid muscles. Cut their interdigitating portions along the median line and reflect them. Find the lateral lobe of the thyroid gland beneath the lateral borders of the sternohyoid muscles. Dissect it, being careful not to destroy the delicate isthmus.

IV. The pharynx (p. 231). Remove the large lymphatic gland between the atlantal transverse process and the larynx. Clean the outer surface of the pharynx. Dissect the muscles of the pharynx (p. 232) as follows:

(_a_) The inferior constrictor (Fig. 96, _k_).

(_b_) The middle constrictor (Fig. 96, _j_).

(_c_) The glossopharyngeus (Fig. 96, _i_).

(_d_) The stylopharyngeus (Fig. 96, _l_).

The superior constrictor cannot well be seen at this point; it will be examined later.

Disarticulate the cranial cornu of the hyoid from the bulla tympani and make an incision the length of the lateral wall of the pharynx so as to expose its cavity; study. Examine its opening into the mouth-cavity and study the general description (p. 231). Find and study the soft palate (p. 230). Dissect the tensor and levator palatini muscles (p. 230, and Fig. 66, _d_ and _e_, p. 112), using, if necessary, the specimen on which the other muscles were dissected. Then slit the soft palate lengthwise at one side of the median line to expose the nasopharynx (p. 231). Bring the choanæ into view by use of a bit of mirror-glass. Pass a bristle into the nares and out at the choanæ. Pass a bristle through the Eustachian tube into the middle ear.

V. Œsophagus (p. 234). After completing the study of the pharynx, leave the larynx and lungs in position and by displacing them toward the right follow the œsophagus to its termination. Open it to see the folds of the mucosa.

VI. Cut through the duodenum at its distal end and through the duodenal mesentery so as to separate the stomach and duodenum, with the liver, pancreas, and spleen, from the remainder of the alimentary canal. Float the parts in a dish of water.

VII. Study the stomach (p. 234, and Fig. 97). Cut out the ventral wall of the stomach and wash it out, so as to study its cavity, and then continue the cut so as to expose the pyloric valve (p. 235).

VIII. Study the duodenum (p. 236). Cut away the ventral walls of the duodenum far enough to expose the ampulla of Vater.

IX. Study the liver (p. 239, and Figs. 100 and 101). Expose the hepatic duct of the left lateral lobe near its entrance into the lobe, and follow it so as to expose it fully. If necessary, prick it and inflate with blowpipe in order to follow it. Then expose the cystic duct and other hepatic ducts and follow them to or from the common bile-duct. Trace the latter to the duodenum. If the air does not enter any duct readily, it may be made to do so by manipulating the duct so as to break up the precipitated bile which obstructs it.

X. Study the pancreas (p. 241, and Fig. 102). Expose the pancreatic duct near its entrance into the ampulla of Vater, by removing the peritoneum from the pancreas just caudad of the end of the common bile-duct, and by dissecting apart the pancreatic lobules until the duct appears. (If possible, expose also the accessory duct in the same way on the ventral side of the pancreas, two centimeters caudoventrad of the ampulla of Vater. Prick and inflate. Trace its connection with the main duct. To demonstrate its opening pass a bristle through an opening in it into the duodenum.) (The pancreatic duct may be injected, if desired.)

XI. The ventral wall of the duodenum should now be removed. Cut out a small piece, clean its mucosa with a fine brush and examine the villi with a lens. Demonstrate the coats of the duodenal wall by stripping them off with forceps.

XII. The ampulla of Vater (p. 236). Pass bristles through openings in the common bile-duct and pancreatic duct into the duodenum through the ampulla. Slice away the duodenal wall parallel to the bristles until the bristles are exposed.

XIII. The spleen (p. 242, and Fig. 102).

XIV. Cut the mesentery from the small intestine and colon and slit them both lengthwise, but do not destroy the ileocolic valve. Wash and brush the mucous membrane clean and study the villi, solitary glands, and Peyer’s patches. Study the ileocolic valve (Fig. 99) and open it to study its inner surface.

DISSECTION OF THE ORGANS OF RESPIRATION.

I. The nasal cavity (p. 243). Review the description of the nasal cavity given under the Bones (p. 59). Study the cartilaginous framework that supports the external nose (p. 243); make a cross-section of the framework near the end of the nose and verify the description (p. 244, and Fig. 103). Without injuring the larynx or tongue saw through the head in a vertical plane and a little to one side of the median line. (If desired, the brain may first be removed from the specimen and preserved for future study. For directions, see page 462. The removal of the brain does not injure the head for the study of the nasal cavity; the skull may be sawn lengthwise in the same way as before.) Wash out the cut surfaces before examining. Find the ventral conchæ (p. 40), the labyrinths of the ethmoid (p. 43), the inferior meatus of the nose (p. 243), and by bristles the lachrymal duct or canal (p. 245). The lachrymal duct is conveniently found by passing bristles into the openings of the lachrymal canals. One of these is to be found on the border of each eyelid, two or three millimeters from the inner angle of the eye (see p. 410).

Cut the œsophagus and trachea at the point where the blowpipe was inserted into the trachea. Separate the tongue, hyoid, larynx, œsophagus, and first part of the trachea from the adjacent parts and remove them.

II. The larynx (p. 246). (1) Read the description, studying the cartilages (p. 247) on a preparation (Fig. 104). Then very carefully remove the pharynx and its constrictor muscles, the sternothyroid and remains of sternohyoid muscles, and (2) dissect the muscles of the larynx (p. 249, and Fig. 105). Dissect all those of one side first. The mucosa lining the vestibule and middle portions of the laryngeal cavity must be removed. After studying the muscles, remove the muscles and entire mucosa by scraping carefully with a dull but smooth scalpel, and study the cartilages (Fig. 104).

III. The trachea and lungs (p. 251, and Fig. 106). The distal end of the trachea and lungs may now be removed with the heart from the body. The lungs may be inflated with the bellows. The bronchi should then be exposed, cleaned, and followed as far as possible into the lungs. The heart should be preserved for future study.

DISSECTION OF THE UROGENITAL ORGANS.

A. _Excretory Organs._

1. Expose the kidney (p. 255, and Fig. 108) by removal of the peritoneum and the surrounding fat, taking care not to open the capsule of the kidney. In removing the fat from the cranial end do not injure the suprarenal body (p. 257), which should be studied.

2. Open the capsule of the kidney and slice away its ventral wall to expose the sinus. After dissecting the contents of the sinus open the pelvis and study the papilla. Pass a bristle from the pelvis into the ureter.

3. Make a median section of the kidney parallel to its ventral surface and study structure (Fig. 109).

4. Trace the ureter to the bladder, being careful not to injure the vas deferens. Study the bladder and its ligaments, structure of its wall, etc. Pass a bristle through the ureter into it and then open it to see the openings of the ureter. Trace the neck of the bladder to the pubis.

B. _Male Genital Organs._

1. Study the external genital organs (p. 257).

2. Carefully remove the integument about the anus and expose the external sphincter ani muscle (p. 268, and Fig. 113, _i_). Trace it to its origin. Remove the integument of the scrotum and dissect the intercolumnar fascia, the levator scroti muscle (p. 271, and Fig. 113, _j_), the tunica vaginalis communis, and propria (p. 258).

3. The testis; the epididymis with great care, especially in uncovering the vasa efferentia; the vas deferens and spermatic cord (p. 259, and Figs. 110 and 111).

4. Follow the cord to the external inguinal ring (p. 259) and expose the ring. Dissect off in order from the inguinal canal: (_a_) The external oblique muscle; (_b_) the internal oblique muscle; (_c_) the transversus. In this way the cord is followed with its tunica communis and tunica propria to the internal inguinal ring.

5. Trace the vas deferens (p. 260, and Fig. 111) within the abdominal cavity as far as it can be seen dorsad of the neck of the bladder.

6. The penis (p. 262, and Figs. 111 and 113). Cut the skin along the dorsum of the penis and reflect. Dissect the ligamentum suspensorium penis. Then introduce a bristle into the urethra and remove the integument from the whole penis and identify the corpora cavernosa and corpus spongiosum and the urethra.

7. Remove the fat at the side of the rectum and find the levator ani muscle (p. 269, and Fig. 162, 11). Transect and reflect it. The internal sphincter ani (p. 269, and Fig. 113, _h_). Find the external opening of the anal gland (p. 239); slit and examine it.

8. Dissect the ischiocavernosus (p. 269) and bulbocavernosus (p. 271) muscles (Fig. 113), and find the bulbus of the corpus cavernosum beneath the former. Cut it free from the ischial ramus.