128 Anatomy of the Rabbit. 



The distinction of medullary and cortical portions depends on differ- 

 ences in the arrangement of the minute tubules which compose the kidney. 

 The medullary substance is largely composed of straight collecting tubules 

 converging on the renal papilla, while the cortical substance is occupied 

 by convoluted portions of the tubules and their vascular connections, the 

 glomeruli. In the natural condition the two parts are also distinguishable 

 in coloration, the cortical substance being darker. In embalmed animals, 

 however, the color features are usually reversed. 



3. The urinary bladder (vesica urinaria) lies in the ventral posterior 

 portion of the abdominal cavity. It is a muscular sac, capable of a 

 considerable amount of distension, but usually found in preserved 

 animals in a greatly contracted condition. Its rounded anterior end, 

 the vertex, projects forward into the abdominal cavity, while its posterior 

 portion or fundus, narrows to a canal, the urethra, which receives on its 

 dorsal wall the apertures of the genital ducts and those of the related 

 glands. The connections may be made out as follows : 



(a) The peritoneum is reflected from the ventral surface of the 

 rectum in the male and from the uterus in the female, to the 

 bladder, and after investing the latter passes to the ventral 

 abdominal wall. The dorsal peritoneum forms in the male 

 a double rectovesical fold (plica rectovesicalis), and in the 

 female a similar vesicouterine fold, a recess of considerable 

 extent (rectovesical or vesicouterine pouch) being left between 

 the adjacent structures. 



The ventral peritoneum forms a broad median vertical sheet, 

 the middle umbilical fold (plica umbilicalis media). The free 

 edge of this fold, extending from the vertex of the bladder to 

 the umbilicus, contains a slender cord, the middle umbilical 

 ligament (lig. umbilicale medium). The latter marks the 

 position of the peripheral portions of the umbilical arteries 

 in the foetus. 



(b) The umbilical artery (a. umbilicalis), a branch of the hypo- 

 gastric, passes along the side of the bladder to the vertex. 

 From the base of the artery branches are given off to the 

 ureter (a. ureterica) and related portions of the genital ducts. 



B. The Male Genital Organs. 



1. Continue the median ventral incision of the skin backward along 

 the symphysis to the penis. Reflect the skin on both sides to clear the 

 attachments of the penis to the ischium, and on the left to a point 

 beyond the scrotum. Note the cremaster muscle (m. cremaster), a thin 

 layer of muscle fibres forming the outer layer of the sac of the testis-. 

 It is continuous with the internal oblique muscle of the abdominal wall, 

 and also contains fibres from the transverse muscle. ■ Make a longi- 

 tudinal incision through this muscle, cutting forward into the abdominal 

 cavity. On spreading apart the two, flaps the following features may 

 be made out: 



(a) The parietal layer (lamina parietalis) of the tunica vaginalis 

 propria, a layer of peritoneum, continuous with that of the 



