114 Anatomy op* thi; Rabbit. 



2. Remove the cutaneus maximus from the surface. Identify the 

 following points of attachment of the abdominal muscles proper: 



(a) The linea alba. 



(b) The linea semilunaris, a slightly curved line situated laterally 

 a short distance from the linea alba. 



(c) The ribs and the costal arch. 



(d) The lumbodorsal fascia (fascia lumbodorsalis), a broad, white 

 sheet of connective tissue extending over the posterior 

 thoracic and lumbar regions. 



(e) The inguinal ligament (ligamentum inguinale), a stout white 

 cord, stretched between the symphysis pubis and the iliac 

 crest. 



3. Identify on the surface the external oblique muscle (m. obliquus 

 externus abdominis). Origin: The posterior ten ribs by separate slips, 

 the xiphoid process, and the lumbodorsal fascia. Insertion: The linea 

 alba and the inguinal ligament. The fibres are directed from an anterior 

 dorsal position downward and backward, the more dorsal ones almost 

 directly backward. Some of the anterior slips of origin interdigitate 

 with those of the thoracic portion of the serratus anterior muscle. Some 

 are concealed by the pectoral muscles. 



The muscle crossing the breast from the sternum to the arm is the pectoralis 

 major. That passing forward from the lumbodorsal fascia to the medial surface of 

 the humerus is the latissimus dorsi. The margins of these muscles may be raised 

 where they conceal the external oblique. 



4. Taking a line between the iliac crest and the xiphoid process, 

 divide the muscle, and then separate it fully from the next, which may 

 be distinguished by the cross direction of its fibres. Note the separate 

 slips of origin and the difference in appearance between the fleshy and 

 aponeurotic portions of the muscle; then remove it from the surface. 



Examine the following muscles, proceeding in a similar manner: 



(a) The internal oblique muscle (m. obliquus internus abdominis). 

 Origin : The inguinal ligament, a second sheet of the lumbo- 

 dorsal fascia, and the posterior four ribs. Insertion: The 

 linea alba. The fibres pass downward and forward. The 

 ventral aponeurosis is much broader than that of the external 

 oblique. It contains the rectus abdominis. 



(b) The transverse muscle (m. transversus abdominis). Origin: 

 Seven posterior ribs, a third sheet of the lumbodorsal fascia, 

 and the inguinal ligament. Insertion : The linea alba. The 

 fibres are directed downward and slightly backward. 



(c) The rectus abdominis muscle. Origin : Lateral border of the 

 sternum, including the xiphoid process; also the ventral 

 surfaces of the second to seventh costal cartilages. Insert- 

 ion : At the anterior end of the pubic symphysis. It is a thin, 

 strap-like muscle, enclosed by the aponeurosis of the internal 



