DISSECTION OF THE DOG 107 



Before any dissection is effected, it is well to examine, as far as possible, the 

 general disposition of the viscera and the arrangement of the peritoneum in 

 the pelvis. 



At the inlet to the cavity the urinary bladder and part of the colon will be 

 encountered. ' The urinary bladder is pear-shaped with its narrow end directed 

 towards the pelvis. When entirely empty the bladder is small in size and firm 

 to the touch. When distended with urine it projects for a variable distance 

 towards the umbihcus, and is generally pushed more or less to one side by the 

 neighbouring intestines. 



The peritoneal covering of the bladder is reflected from the organ in the 

 form of three sheets. One of these (plica pubovesicalis) is ventral in position, 

 triangular in form, extensive and thin. The other two are lateral in position 

 (plicae vesicales transversse) , are also triangular, and contain the ureters. 



The two deferent ducts in their course from the abdominal ring of the 

 inguinal canal lie dorsal to the neck, or narrow pelvic end, of the bladder. 

 Each duct is contained in a fold of peritoneum, and the two ducts are united 

 dorsal to the bladder by a triangular peritoneal fold with a free cranial base. 

 Close to its termination each duct is crossed laterally by the ureter. 



The termiaal part of the colon is dorsal to the bladder. The peritoneal 

 investment is more extensive on the dorsal aspect of the bladder — where it is 

 reflected onto the termination of the colon — than it is ventral to this organ. 

 About the pelvic inlet the peritoneum generally covers a considerable 

 accumulation of fat, on the removal of which the prostate is exposed. 



Dissection. — Clean the muscles away from one hip bone. Liberate the 

 root of the penis from the ischium. Cut along the symphysis of the 

 ischia and pubes, and snip through the ihum immediately cranial to the 

 acetabulum. This will isolate a piece of bone consisting of ischium, 

 pubis, and part of the ilium. Remove this carefully. In doing so it 

 will be necessary to cut through the origins of the levator ani, coccygeus 

 and ischio-urethral muscles. Stumps of these should be left attached 

 to the bone for examination at the proper time. Now clean the lateral 

 surface of the pelvic organs, preserving the vessels and nerves and observing 

 the arrangement of the peritoneum. 



M. COCCYGEUS. — The coccygeus muscle is the most lateral of a group 

 contained within the pelvis. From their origin from the margin and medial 

 aspect of the sciatic spine, the fibres of the muscle run towards the tail, diverging 

 somewhat as they go, and are inserted into the transverse processes of the 

 coccygeal vertebrae from the second to the fifth. 



Intbstinum rectum. — The last part of the large intestine is a short and 

 approximately straight tube continuing the colon through the pelvis and 

 terminating at the anus. Externally the tube is even, and shows the course of 

 longitudinal muscle fibres. Suspended from the mid-dorsal fine by a narrow 



