Illustrated Encyclopedia of Human Anatomic Variation: Opus III: Nervous System
Ronald A. Bergman, PhD
Adel K. Afifi, MD, MS
Ryosuke Miyauchi, MD
Peer Review Status: Internally Peer Reviewed
Fig. 1. Sternalis muscle in a female subject. Drawing taken from a preparation preserved in Anatomy Department of Trinity College
Dublin. a., sternalis with intercostal nerves hooking round its inner margin; p., pectoralis major; c., internal anterior thoracic nerve; d., pectoralis minor; e. cords of brachial plexux; f., external anterior thoracic nerve; g., pectoralis major; i., sternal head of sternomastoid.
Fig. 2. Double sternalis in male subject. Relation of intercostal nerves displayed. On each side two nerves pierce the great pectoral muscle and run inwards. On the left side both reach the sternalis; on the right side the upper of the two exhausts itself in branches to the great pectoral before it reaches the sternalis.
Fig. 3. Dissection under water of the anterior thoracic nerves and the connecting arch. i.a.t., internal anterior thoracic nerve; e.a.t., external anterior thoracic nerve; P. maj., branches to pectoralis major; P. min., branches to pectoralis minor; s., branch to sternalis.
At that time I had observed no case of the sternalis in the male, but had seen it five times in the female.
It will be noticed that, through the medium of the connecting arch, fibres from both nerves reach not only the sternalis but also the pectoralis minor.
Fig. 4. Very remarkable case of unilateral sternalis in a male. The muscle is split into two parts, and the inner portion has wandered inwards so as to lie over the inner margin of the sternum. The recurrent course of the intercostal nerves is very conspicuous.
Fig. 5. Sternalis muscle in a male subject, with all the nerve relations exhibited. I.A.T., internal anterior thoracic nerve ; E.A.T., external anterior thoracic nerve P.M., pectoralis minor; S.P., sternal part of pectoralis major.
From Cunningham, (1888) The musculuc sternalis. J. Anat. Physiol. 22:391-407.
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