Charles Eussell Bardeen 205 



(10.6^); and to the 11th in 56 out of 79 instances (70. 9j^). In no in- 

 stance have I seen a transverse tendon corresponding to the 13th rib. 



In the simple conditions where the segments of the rectus are dis- 

 tinct and the transverse tendons well marked, the abdominal nerves 

 after emerging from the intercostal spaces take a fairly direct course 

 to the lateral margin of the rectus. Each nerve then pierces the rectus 

 sheath, courses along the under surface of the latter muscle, and then 

 gives off one or more cutaneous branches which usually emerge through 

 the rectus in the vicinity of the transverse tendon corresponding to the 

 rib by which the nerve is designated, and one or more muscular branches 

 which are distributed to the segment of the rectus distal to that trans- 

 verse tendon. The region where the rectus sheath is pierced by a given 

 spinal nerve is usually posterior to the corresponding transverse tendon 

 in case of the 7th and 8th nerves, and anterior in case of the 10th, 11th 

 and 12th nerves. In a recent article in this journal * it has been shown 

 that the primary ventral cutaneous branches of the more distal thoracic 

 nerves are caught between the successive tips of those myotomes which 

 give rise to the rectus musculature, and that in this way, the segmental 

 arrangement of the nerves of the abdomen is early insured. In those 

 instances in Avhich no transverse tendon is developed in the region 

 between the tips of two myotomes, the tissue derived from each myotome 

 is fused to a considerable extent, and the corresponding nerves are less 

 definitely guided in their growth. We find, therefore, in the adult far 

 greater irregularity in the course and in the distribution of the branches 

 of such nerves. Often two or more nerve trunks, arise from a single 

 intercostal nerv^e, and course forward to pierce the rectus sheath sepa- 

 rately. See Fig. II. This was found to be the case with the 8th 

 nerve, in 2 out of 37 instances; with the 9th in 3 out of 61; with the 10th 

 in 6 out of 85; with the 11th in 18 out of 79 instances; and with the 

 12th in 17 out of the 56 instances in which the twelfth furnished no 

 direct hypogastric branch. In 18 instances, out of the 74 in which a 

 careful record was made of the branches of the 12th thoracic nerve, 

 the nerve sent a ventral branch to the rectus, and a separate hypogastric 

 branch to the skin of the abdomen. See Fig. Ill A. 



Not infrequently an abdominal nerve will divide into two or more 

 branches immediately before entering the rectus sheath. See Fig. I C. 



In the majority of instances, as pointed out by Mall (op. cit.), the 

 transverse tendon of the rectus corresponding to the 10th rib is attached 



4 Bardeen and Lewis: Development of the limbs, body-walls and back in man. This 

 journal, Vol. I, 1901, p. 1. 



