Part 101

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.