88 TOPOGRAPHICAL ANATOMY OF THE 



close to the pubis. Just cranial to the prepuce of the male, or the 

 mammary glands of the female, there is an inconspicuous scar, the 

 umbilicus, marking the point of attachment of the umbilical cord of 

 embryonic life. 



Dissection. — If the dissection has been performed in accordance with 

 the instructions given on the preceding pages, the whole thickness of 

 the abdominal wall will still be undisturbed on one side of the body ; 

 while, on the other side, the lining membrane (the peritoneum) and its 

 supporting fascia will alone need incision in order that the abdominal 

 cavity may be opened. 



Now open the abdomen in the following manner : — Make an incision 

 along the linea alba from end to end. Then make a transverse incision 

 through the peritoneum on the one side, and through the intact wall 

 on the other, about midway between the level of the last rib and the 

 pecten of the pubis. 



On that side of the body on which the abdominal wall has not been 

 dissected, the form, course and general anatomy of the inguinal canal 

 should be studied. Begin by making a thorough examination of the 

 intact canal, afterwards performing such dissection as is necessary to 

 display its various boundaries, relations and contents. 



The inguinal canal (Canalis inguinalis). — The inguinal^ canal, 

 some 10-12 cm. in length, is a curved, oblique passage, or flattened tube, 

 lined by peritoneum, that traverses the abdominal wall and contains the 

 spermatic cord, with the external cremaster muscle, in the male. In 

 the mare it is rarely the case that a tubular diverticulum of the peri- 

 toneum enters the canal. 



The course of the canal is ventral, medial and slightly cranial, with 

 a flat curve the concavity of which looks in a cranial direction. Its 

 caudo-lateral wall is formed by the inguinal ligament of Poupart ; while 

 the opposite (cranio-medial) wall mainly consists of the fleshy part of 

 the internal oblique abdominal muscle. The external opening of the 

 canal (annulus inguinalis subcutaneus) is essentially a slit, 10-13 cm. 

 long, in the aponeurosis of the external oblique muscle, running obliquely 

 in a lateral and cranial direction in conformity with the course of the 

 aponeurotic fibres. The medial end of the slit is sharply defined by the 

 strong pubic attachment of the tendons of the two recti muscles. The 

 lateral extremity is less definite. For surgical reasons it should be 

 remembered that, though the lips of the opening are at no great distance 

 apart when the limb occupies the position of rest, it is possible to widen 

 the opening to some extent by drawing the limb into a position of ex- 

 tension of the hip joint. 



The inner or deep opening of the canal (annulus inguinalis ab- 

 dominalis) is an oval space in the transverse fascia of the abdominal wall 



^ Inguinalis [L.], pertaining to the groin ; inguen [L.], the groin, the organs of 

 generation. 



