426 



Mr. W. P. Herringham. 



of the acromial thoracic artery, to supply the pectoralis major ; the 

 other goes behind the pectoralis minor, sends two twigs through it 

 which supply it and the next parts of the pectoralis major, and close 

 to the lower border of the muscle joins with the internal anterior 

 thoracic which appears from under the artery. The united nerve now 

 supplies the lowest part of the pectoralis minor, and turning round 

 its edge serves the lowest fibres of the pectoralis major. 



This arrangement was constant in eight consecutive adult cases that 

 I dissected. I was, however, able in one of the foetal dissections to 

 see more than this. The branch from the 5th and 6th, before joining 

 the branch from the 7th, gave a twig which ran to the clavicular 

 portion and which alone supplied that part. The union of the 5th, 

 6th, and 7th supplied the upper part of the sternal muscle. The 7th 

 served the middle as in the adult, but the internal anterior thoracic 

 before receiving the 7th gave off a twig which supplied the lowest 

 fibres of the pectoralis major, its union with the 7th serving the fibre 

 next in order above these. 



Of the nerves interested in the anterior thoracics the 7th always 

 contributes. Of thirteen dissections the 5th and 6th both gave 

 branches to the external in five, the 6th alone in eight cases. Of ten 

 dissections the 8th and 9th both gave branches to the internal in eight 

 cases, the 8th alone in two. It appears, therefore, that the pectoralis 

 major does not usually receive from the 5th, and does usually receive 

 from the 9th.* 



Below these branches the 7th joins the 5th and 6th, thus forming 

 the outer cord, which bifurcates into the musculo-cutaneous and the 

 outer head of the median. I have seen three cases where the musculo- 

 cutaneous when about to pass under the biceps to the outer side of 

 the arm gave back a large bundle to the median. Two of these cases 

 were adult, and in them the returned bundle consisted in one wholly 

 of the 6th root, in the other of fibres from both 6th and 7th. 



The musculo-cutaneous is usually described as supplying the coraco- 

 brachialis. In the adult the nerve to this muscle is given off before 

 the musculo-cutaneous enters it. If traced up it is seen to come from 

 the outer cord before the musculo-cutaneous leaves it, and ultimately 

 from the 7th root in the outer cord. It passes under the cord to get 

 to the muscle. 



Here again the system is very much clearer in the foetus, for in the 

 foetal plexus the coraco-brachial nerve can be seen running from the 

 7th before it joins the 5th and 6th, and passing under the 5th and 



* The first dorsal I have here called, and shall henceforth call, the 9th spinal 

 root, the 2nd and 3rd dorsal the 10th and 11th respectively. The 9th receives at its 

 origin a small branch from the 10th in the majority of cases. It is too small to 

 dissect in the foetus, and the conditions of a dissecting room do not allow of its 

 dissection in the adult. 1 have therefore included it in the 9th root. 



