8 DISSECTION OF THE DOG 



consists of two layers : a double parietal layer, and a visceral layer intimately 

 adherent to the glans penis. The superficial sheet of the parietal layer is 

 composed of skin differing little from that of the neighbourhood. This should 

 be reflected by making a longitudinal incision from the preputial orifice to 

 the scrotum. Care must be taken to preserve the preputial muscle (m. prse- 

 putialis) which, as a flattened band, springs from the abdominal aponeurosis 

 in the xiphoid region, and runs immediately under the skin to form a loop 

 round the orifice of the prepuce. 



If the deep sheet of the parietal layer be now slit open with a pair of scissors, 

 its resemblance to mucous membrane will be manifest. The surface looking 

 towards the penis is longitudinally folded and studded with irregular rows 

 of flattened, rounded elevations caused by masses of lymphoid tissue. The 

 membrane is directly continuous with the visceral layer of the prepuce, which 

 extends over the glans penis to the urethral orifice where it meets the urethral 

 mucous membrane. 



It should now be noted that the prepuce is supplied with blood by the 

 external pudendal artery. 



Dissection. — The penis should now be freed from its surroundings as far as 

 its root. In cleaning the organ, note the presence of a narrow, pale 

 muscle, the retractor of the penis, running along its urethral surface 

 from the anus to the vicinity of the glans. Preserve also the dorsal 

 vessels and nerves which will be found on the opposite surface. 



Penis. — The penis consists of a middle part (its body or corpus penis), a 

 root (radix penis) attached to the arch formed by the two ischial bones, and a 

 free extremity (glans penis) of considerable length. 



The term dorsum penis is applied to that aspect of the organ which is in 

 contact with the abdominal wall ; whereas the opposite aspect is called the 

 urethral surface (facies urethralis). 



The body of the penis lies in the middle line, dorsal to the testes and crossed 

 laterally by the ductus deferens. It is composed of three bodies running 

 parallel to each other. 



The corpora cavernosa penis are two rods of erectile tissue surrounded and 

 bound together by a dense fibrous envelope, the tunica albuginea [corporum 

 cavernosorum], and separated from each other by a fibrous septum (septum 

 penis). In the ischial region the two corpora diverge, each forming a crus 

 penis which is attached to the border of the ischium. From about the middle 

 of the penis, the corpora are continued onwards as a bone, the os penis. This 

 may be considered as formed by two narrow plates joined dorsally and diverging 

 ventrally to enclose a groove in which the urethra lies. The caudal end of the 

 bone is truncated. The cranial end is more pointed, and to it is appended a 

 curved process composed of fibrous tissue of cartilage-like density. 



The third erectile body of the penis is the corpus cavernosum urethrce, 



