294 THE ANATOMY OP THE HORSE. 



former enters the inguinal canal at a point internal to the internal 

 abdominal ring. The latter passes behind the ring, and crosses it on 

 the inner side. Both branches have already been followed, but the 

 relation of the posterior abdominal artery to the ring should now be 

 specially noted, as, in consequence of its position, an incision for the 

 rehef of a strangulated hernia must be made outwards to avoid wound- 

 ing the vessel. 



The Spermatic Cord. The various structures which compose the 

 spermatic cord meet at the internal abdominal ring. The vas deferens 

 is seen tiuning inwards to enter the pelvis, and projecting the peri- 

 toneum to form a small band, or frsenum, for itself. The vessels and 

 nerves of the cord are to be left undisturbed, so that they may be followed 

 to their source at a later stage. 



The Cremaster Muscle (Plate 44). The fibres of this muscle are 

 now seen at their origin from the iliac fascia, where they are close to, the 

 muscular fibres of the internal oblique. They pass into the inguinal 

 canal, where, separating but remaining connected by intermediate 

 areolar tissue, they constitute the cremasteric covering of the cord and 

 testicle. When the muscle contracts, it twitches the testicle upwards 

 by shortening the spermatic cord. 



THE CAVITY OP THE ABDOMEN. 



Boundaries of the Cavity. — The abdomen is the largest of the visceral 

 cavities of the body. It is placed behind the thorax, from which it is 

 separated by the diaphragm ; posteriorly it is directly continuous with 

 the cavity of the pelvis ; laterally and inferiorly it is enclosed by muscu- 

 lar, tendinous, and elastic textures making up what is generally termed 

 the abdominal wall; and superiorly it is bounded by the lumbar portion 

 of the spine clothed by the sublumbar muscles. 



Contents of tlie Cavity. — The cavity is occupied mainly by the gastro- 

 intestinal part of the alimentary tube, and its associated glands — the 

 liver and the pancreas. Besides these, it lodges the spleen and the 

 kidneys. In the female it contains the ovaries and the uterus (in part), 

 and in the male the vas deferens passes through it. 



Divisions of the Cavity. — As a matter of convenience in describing the 

 position of its contained organs, the cavity is arbitrarily divided into the 

 following nine areas : — 



This subdivision is quite arbitrary, the boundaries between these areas 

 being certain imaginary planes. Thus, the three anterior regions are 

 separated from the three middle regions by a transverse vertical plane 

 passing through the lower end of the 15th rib, and the three middk 



