PRACTICAL DIRECTIONS. 455 



3. Examine the cervix uteri and os uteri (p. 266). 



4. Introduce a probe through the neck of the bladder and note 

 its emergence into the urogenital sinus. 



5. Find the end of the clitoris (p. 267), and its prepuce, and then 

 dissect the integument carefully from about the external opening of 

 the urogenital sinus and note an external sphincter of the sinus 

 (M. levator vulvae) (p. 272, and Fig. 114), equivalent to the levator 

 scroti in the male and continuous with the external sphincter ani. 



6. Find (if possible) the corpora cavernosa of the clitoris 

 (p. 267) and the ischiocavernosi muscles (p. 269). 



DISSECTION OF THE CIRCULATORY SYSTEM. 

 I. THE HEART (p. 274, and Figs. 115 117). 



Use the heart from the specimen dissected for the muscles, or 

 from the specimen on which the viscera were studied.' 



1. Study the outside (p. 275, and Figs. 115 and 116), and learn 

 to recognize all parts. Find the pulmonary veins (p. 275, and Fig. 

 116, g, h, z') and cut them, thus separating the heart from the lungs. 



2. The Pericardium (p. 279). In a specimen the thoracic con- 

 tents of which have not been injured, dissect the mediastinal septum 

 from the pericardial sac and remove fat about the great blood-vessels 

 so as to expose them all fully. Study their relations. Prick and 

 inflate the pericardium. Slit it lengthwise over the ventricles and 

 reflect it so as to expose its contents. Study the attachment of 

 serous and fibrous layers to the heart and their relation to one 

 another. 



3. In dissecting the heart follow the course of the blood, study- 

 ing each cavity with the aid of the descriptions (pp. 275-279) as you 

 proceed. Dissect as follows : 



a. Remove the dorsal wall of the right auricle (p. 275) and of its 

 appendage except that part of it to which the venae cavse are 

 attached. 



b. Introduce the probe from the right auricle into the right ven- 

 tricle, and feel with the probe the line along which the ventricular 

 wall joins the septum. Cut along this line so as to turn back the 

 ventricular wall as a flap, which remains attached at the base of the 

 ventricle. 



c. Introduce a probe through the conus arteriosus into the 

 pulmonary artery and cut along the probe. 



d. Remove the dorsal wall of the left auricle and its appendage, 

 but do not remove that part to which the pulmonary veins are 

 attached. 



e. Make a longitudinal incision beginning at the apex and divari- 

 cate the lips of the cut as you pass toward the base, thus avoiding 

 injury to the lateral flap of the bicuspid valve. Without injury to 

 the flap or the columnae carneae, remove the heart-wall at the sides of 

 this incision near the base of the ventricle, as much as necessary to 

 expose the cavity. 



