204 Study of the Abdominal and Border-Nerves in Man 



between the muscles of the abdominal wall, and finally are distributed 

 in part to the rectus musculature and in part pass through the latter 

 to be distributed to the skin. The last intercostal nerve confined to 

 the thorax is distributed in part to the thoracic segment of the rectus 

 knd in part to the overlying skin, while the ventral branches of the 

 more anterior intercostal nerves pass through, the overlying structures 

 directly to the subcutaneous tissue. It is probable that occasionally 

 more than one thoracic segment of the rectus muscle is developed 

 in man. Such, however, has not been the case in the subjects which 

 I have examined. As shown in the table, in 10 instances the 6th 

 nerve was the nerve distributed to the thoracic segment of the 

 rectus, and in 6 instances the 7th. The first nerve passing below the 

 costal margin before entering the rectus (that is to say, the first abdom- 

 inal nerve) was in 10 instances the 7th, and in 6 instances the 8th nerve. 

 A record was preserved of the race, sex, side of body, skeletal condi- 

 tions, position of the lumbo-sacral plexus and of the border-nerves in 

 the instances studied. No marked relation seems to exist between any 

 of these factors and the variations noted in the table. 



Eelations of the Abdominal Nerves to the Teansverse Ten- 

 dons (Linea transversa, Inscription es tendinece) OF the Eectus Abdoim- 

 iNis Muscle. See Table II. — The transverse tendons of the rectus 

 abdominis muscle in man correspond to the 7th, 8th, 9th, 10th, 

 and 11th ribs.^ The relation between the transverse tendons and the 

 costal cartilages is best seen in the transverse tendons corresponding to 

 the seventh and eighth cartilages. In this region the bundles of fibres 

 making up a segment of the rectus originate or terminate in part on the 

 costal cartilage, in part in the corresponding tendon. The transverse 

 tpndons corresponding to the eighth costal cartilage are often, to the 

 ninth are usually, and to the tenth and eleventh are always some dis- 

 tance removed from the corresponding costal cartilage. 



In the adult individual the transverse tendons are often to a greater 

 or less extent obliterated, owing to the unequal growth of muscle-fibre 

 bundles, some of which extend over more than one segment. Tlie 

 transverse tendon corresponding to the 7th costal cartilage has been 

 fairly distinct in all of the instances I have examined, but that corre- 

 sponding to the 8th was absent in 9 out of 37 instances (24.3^); to the 

 9th in 4 out of 62 instances (6.5^); to the 10th in 9 out of 85 instances 



3 See Mall, Devel. of the Ventral Abdominal Walls in Man, Journal of Morphology, 

 Vol. XIV, p. 2, 1898. 



