Morphometry and Frequency of the Pyramidalis Muscle in Adult Humans: A Pyramidalis Muscle's Anatomical Analysis

Abstract

OBJECTIVES: To verify the pyramidalis muscle’s frequency (bilaterality, unilaterality, or absence) and morphometry (length of the medial border and width of its origin/base) in a sample of the Brazilian population and the anthropometric influence. METHODS: Dissection of 30 cadavers, up to 24h post-mortem. RESULTS: The pyramidalis muscle was present bilaterally and unilaterally in 83.33% and 3.33% of the cadavers, respectively, and absent in 13.33%. The muscles on the right and left sides were symmetrical in length but not in width; the pyramidalis muscles of men were longer, while those of the women were wider. We also found that there was greater variation in the dimensions (length and width) of the men’s muscles. Finally, in this sample of the Brazilian population, the pyramidalis muscle’s unilaterality was more prevalent than in other populations, and its complete absence was less prevalent. CONCLUSIONS: There were no cases of muscle duplication in one or both sides, as described in some studies. Despite all of its morphometric variation, the pyramidalis muscle maintained its triangular shape with longitudinal fibers in every case. Furthermore, no statistically significant correlation was noted between the muscles’ dimensions and person’s age, height, weight, or gender.

Reappraisal of the anatomical diversity of the pyramidalis muscle with its substantial clinical applicability: Cadaveric analysis

“…The difference may be due to racial variations i.e., differences of stature in different populations. On contrary, the average muscle width was pretty near to the values reported in the Nigerian and Greek populations [26,27] and lesser than the Brazilian and northern Indians [5,12]. Statistically signi cant sexual dimorphism was found based on muscle length and width (Table 1).…”

“…Every single biometric parameter of the PM was greater on the right side than the left side except the angle of insertion which was greater on left (Table 1). The average lengths in both genders were almost half of the mean value reported in the corresponding Greek, Nigerian and Brazillian ethnicity [8, 12,26] and almost equal to the north Indian population [5,14]. The difference may be due to racial variations i.e., differences of stature in different populations.…”

“…Its phylogenetic origin has not yet been truly elucidated, which makes it di cult to ascertain its developmental process [4]. While some studies say that the PM is a vestigial muscle phylogenetically derived from monotremes thus tending to disappear in the future, others believe it to be a newly formed structure in the primate, reaching its highest development in man [3], others argue that its presence is related to the erect posture [12] and thus tends to become more prevalent.…”

“…It is believed that the action of the PM is to tighten the linea alba and strengthen the abdominal wall [20,21], however occasionally this action is useless, hence, some authors consider it a vestigial, leftover from the marsupials' and monotremes' pouch [7,29], evolving into an irregular apparition in more evolved primates, often observed in chimpanzees and gorillas but absent in orangutans [19,31]. There are also anthropological studies suggesting that the PM has evolved as part of the normal human anatomy, in which case it could be related to the species' erect posture [12].…”

Anatomy of the anterior jugular veins: anatomical study of 30 cadavers

“…Although 30 cadavers may seem a small sample size for anatomical studies, this number has been proved representative for an initial evaluation in previous studies conducted by our research group [8][9][10] . Our findings show a high frequency of anatomical variations of the AJVs, mainly related to number and location.…”