12 DISSECTION OF THE DOG 



doing so observe its firm attachment to the tendinous intersections of the 

 underlying straight muscle. Cut across the fleshy part of the internal 

 oblique muscle in the same manner as was done with the external oblique. 

 Reflect the transverse muscle of the ribs. 



M. bectus abdominis. — The fibres of the straight muscle of the abdomen 

 run parallel to the middle line of the body. Generally six tendinous inter- 

 sections cross the muscle in an irregularly oblique manner. Of these one 

 occurs on a level with the umbilicus ; two are caudal, and three are cranial 

 to this point. As has already been seen, the superficial sheath of the muscle 

 is firmly adherent to the intersections. 



The cranial attachments of the rectus muscle are by means of a thin aponeu- 

 rotic tendon (partly covered by the expanded insertion of the m. transversus 

 costarum) from the cartilage of the first rib, and from the sternal end of the 

 cartilages of the ribs from the second to the seventh. In addition fleshy slips 

 leave the sternal ends of the eighth and ninth ribs. 



Caudally the muscle is attached to the border of the pubis. 



Dissection. — Reflect the straight muscle by a transverse incision about 

 the middle of its length, and thus expose the cranial and caudal epigastric 

 vessels as well as certain intercostal and lumbar nerves and vessels. 



A. epigastrica catjdalis. — The caudal epigastric artery either arises in- 

 dependently from the deep femoral artery, or it has an origin in common with 

 the external pudendal. The artery lies on the deep face of the rectus muscle 

 of the abdomen and runs in a cranial direction. It is accompanied by the 

 caudal epigastric vein (v. epigastrica caudalis). 



A. et v. epigastrica cranialis. — The cranial epigastric vessels appear 

 between the xiphoid process of the sternum and the ninth or tenth costal 

 cartilages ; that is, not far from the middle line. They follow a slightly oblique 

 direction on the deep surface of the rectus muscle. Superficial branches, 

 piercing the muscle or crossing its medial border in the xiphoid region, have 

 already been noticed. 



Nerves of the Abdominal Wall. — Lying deep to the internal oblique 

 and rectus muscles on the one hand, and superficial to the transverse muscle 

 on the other, are branches of the last five thoracic and the first two lumbar 

 nerves. 



The last four intercostal nerves are derived from the ventral primary divisions 

 of the ninth, tenth, eleventh, and twelfth thoracic nerves. They appear from 

 beneath the costal arch, cross the surface of the transverse muscle, and 

 disappear under the rectus. The last thoracic nerve is similarly disposed. 



The ilio-hypogastric and ilio-inguinal nerves arise from the ventral primary 

 divisions of the first two lumbar nerves. 



N. ilio-hypogastricus. — The ilio-hypogastric nerve divides into lateral and 



