Content uploaded by Aroa Casado
Author content
All content in this area was uploaded by Aroa Casado on Aug 10, 2020
Content may be subject to copyright.
ANATOMICAL VARIATIONS OF THE PECTORALIS MINOR MUSCLE IN
HOMINOID PRIMATES
1. INTRODUCTION
In humans, the pectoralis minor originates from the third, fourth and fifth ribs and inserts at
the coracoid process. In hylobates, it inserts at the coracoid process or the clavicle (Diogo
et al., 2012). In orangutans, the pectoralis minor inserts at the coracoid process, the
proximal humerus, or the glenohumeral capsule (Diogo et al., 2013a).In gorillas and
bonobos, it inserts at the coracoid process (Miller, 1952; Diogo et al., 2010), and in
common chimpanzees at the proximal humerus, the glenohumeral capsule (Diogo et al.,
2013b), or less frequently, the coracoid process (Diogo and Wood, 2012). The main
variation of the pectoralis minor in humans is its insertion point, which can be the
glenohumeral capsule, the greater tubercle of the humerus, or the coracoacromial
ligament (Tubbs et al., 2005). The pectoralis minor can also insert at the supraspinatus
tendon (Uzel et al., 2008).
We have analyzed the morphological characteristics of the pectoralis minor in different
species of hominoid primates, including humans (Figure 1). Our objective is to gain a
better understanding of the anatomy of this muscle and its variations in the primate
species most closely related phylogenetically to humans. A detailed analysis of the
pectoral muscles and their possible variations in hominoid primates will also provide
valuable information on the anatomic variations of these muscles in humans, especially
the variations on insertion of the pectoralis minor, which have been related to the
ethiopathogenesis of some diseases such as the subacromial impingement syndrome
(Uzel et al., 2008)and to some surgical complications (Beser et al., 2013).
2. MATERIAL AND METHODS
We have macroscopically dissected the pectoral region in four hylobatids (two Nomascus gabriellae, one Hylobates lar and one Symphalangus syndactylus), three orangutans (Pongo pygmaeus), three
gorillas (Gorilla gorilla), six common chimpanzees (Pan troglodytes), five bonobos (Pan paniscus)and five humans (Homo sapiens). All specimens were frozen 24 hours post-mortem and stored at -27ºC until
they were dissected. They were not treated with any fixation method. All the hominoid primates were dissected at the Anatomy Museum of the University of Valladolid (Spain) and the bonobos at the Veterinary
School of the University of Antwerp (Belgium). All the apes died from causes unrelated to this study. The five humans were cadavers from the Body Donation Service and Dissection Rooms of the University of
Barcelona and were dissected at the Anatomy and Embryology Unit of the School of Medicine of the University of Barcelona (Spain).
4. REFERENCES
Andrews P, Groves CP (1976) Gibbon and brachiation. In Gibbon and Siamang (ed. Rumbaugh DM). Basel: Karger. Beser CG, Ercakmak B, Tunali S, Basar R (2013) Combination of six variations in a single arm. Rom J Morphol Embryol 54,845-849.Diogo R, Wood BA (2012)Comparative anatomy and phylogeny of primate muscles and human evolution. Boca Raton: CRC Press. Diogo R, Potau JM, Pastor
JF, et al.(2010)Photographic and descriptive musculoskeletal atlas of gorilla with notes on the attachments, variations, innervation, synonymy and weight of the muscles. Boca Raton: CRC Press. Diogo R, Potau JM, Pastor JF, et al.(2012)Photographic and descriptive musculoskeletal atlas of gibbons and siamangs (Hylobates) with notes on the attachments, variations, innervation, synonymy and weight of the
muscles. Boca Raton: CRC Press. Diogo R, Potau JM, Pastor JF, et al.(2013a) Photographic and descriptive musculoskeletal atlas of orangutans with notes on the attachments, variations, innervation, function and synonymy and weight of the muscles. Boca Raton: CRC Press. Diogo R, Potau JM, Pastor JF, et al.(2013b) Photographic and descriptive musculoskeletal atlas of chimpanzees with notes on the
attachments, variations, innervation, function and synonymy and weight of the muscles. Boca Raton: Taylor & Francis. Goldman E, Vasan C, Lopez-Cardona H, Vasan N (2016) Unilateral ectopic insertion of the pectoralis minor: clinical and functional significance. Morphologie 100,41-44.Hatakeyama Y, Itoi E, Urayama M, Pradham RL, Sato J (2001) Effect of superior capsule and coracohumeral ligament
release on strain in the repaired rotator cuff tendon. A cadaveric study. Am J Sports Med 29,633-640.Miller RA (1952) The musculature of Pan paniscus.Am J Anat 91, 182-232.Moineau G, Cikes A, Trojani C, Boileau P (2008) Ectopic insertion of the pectoralis minor: implication in the arthroscopic treatment of shoulder stiffness. Knee Surg Sports Traumatol Arthrosc 16,869-871. Tubbs RS, Oakes WJ, Salter
EG (2005) Unusual attachment of the pectoralis minor muscle. Clin Anat 18,302-304.Uzel AP, Bertino R, Caix P, Boileau P (2008) Bilateral variation of the pectoralis minor muscle discovered during practical dissection. Surg Radiol Anat 30,679-682.
JM. Potau1, A. Casado1, M. Gómez1, J. Arias-Martorell1,2, G. Bello-Hellegouarch1,3, M. Barbosa4, F. de Paz4, JF. Pastor4
1. Unit of Human Anatomy and Embryology. University of Barcelona. Barcelona. Spain.
2. Animal Postcranial Evolution Lab. Skeletal Biology Research Centre. University of Kent. UK.
3. Department of Biology. University of Sao Paulo. Sao Paulo. Brazil.
4. Department of Anatomy and Radiology. University of Valladolid. Valladolid. Spain.
This study was supported by the Ministerio de Economía y Competitividad of Spain (project CGL2014-52611-C2-2-P) and the European Union (FEDER)
Fig 1. Dissection of the pectoralis minor muscle in Homo sapiens (*)
Fig 4. Dissection of the pectoralis minor (*) in Pan paniscusFig 3. Insertion of the pectoralis minor in Pan troglodytes
(Pm=pectoralis minor; ST=supraspinatus tendon;
GHC=glenohumeral capsule)
Fig 2. Dissection of the pectoralis minor (*) in Gorilla gorilla
*
*
*
3. RESULTS AND DISCUSSION
We found that in the hylobatids, orangutans and gorillas the pectoralis minor inserts on the coracoid process of the scapula (Figure 2). In Pan troglodytes, the most commonly observed point of insertion is
near the humerus or at the glenohumeral capsule (Diogo et al., 2013b), although some studies have reported a complete or partial insertion at the coracoid process of the scapula (Andrews and Groves,
1976). In the present study, all the Pan troglodytes had the same, relatively unusual, pattern of insertion: the tendon of the pectoralis minor passed over the coracoid process and finally inserted at the
supraspinatus tendon (Figures 3). In all our Pan paniscus specimens, the pectoralis minor inserted at the coracoid process of the scapula (Figure 4), which is in line with an early report by Miller (1952). Like
the bonobos, the most frequent point of insertion of the pectoralis minor in Homo sapiens is the coracoid process of the scapula, though other insertion points have also been reported, including the
glenohumeral capsule, the greater tubercle of the humerus, and the coracoacromial ligament (Goldman et al., 2016). In two of our Homo sapiens specimens, the pectoralis minor inserted at the glenohumeral
capsule after passing over the coracoid process (Figure 5). The pectoralis minor has also been reported to insert at the supraspinatus tendon in humans (Uzel et al., 2008), which is similar to our findings in
Pan troglodytes. Several studies have found that anomalies in the insertion of the pectoralis minor in humans are related to subacromial impingement (Hatakeyama et al., 2001), to shoulder pain and stiffness
and to a limited lateral rotation of the glenohumeral joint (Moineau et al., 2008).
*
*
Fig 5. Unusual insertion of the pectoralis minor in Homo sapiens
(Pm=pectoralis minor; ST=supraspinatus tendon;
GHC=glenohumeral capsule; CP=coracoid process)