Bony ponticles of the atlas (C1) over the groove for the vertebral artery in humans and primates: Polymorphism and evolutionary trends

Abstract

The aim of this study was to ascertain the distribution in primates of the three possible bony ponticles over the groove for the vertebral artery (ventral, lateral, and dorsal ponticles), in order to attempt to understand the variants observed in humans and to ascertain possible evolutionary trends in primates. The material consisted of 393 atlases of extant nonhuman primates representative of 41 genera, and of 500 human atlases (dried bones of adults). For each atlas, we studied the existence and morphology of the ponticles, and the type of association of these three ponticles on a given side, which are theoretically of eight in number (types A-H). The occurrence of these ponticles varied from complete absence to constant presence, according to the genera and taxa of primates. The presence of each of these ponticles in primates can be interpreted as a primitive or plesiomorphic character, and their absence as a derived or apomorphic character. The strepsirhines-platyrrhines-cercopithecines group, presenting a predominant primitive pattern (type A), appeared to be separated from the colobines-hominoids group, presenting predominant derived patterns (type C in colobines, Pongo pygmaeus, and Pan troglodytes, and the more derived type D in Hylobates, Gorilla gorilla, and Homo sapiens). The last derived stage, corresponding to the disappearance of the three atlantal ponticles (type H), was only observed in some individuals in hominoids. A marked intraspecific polymorphism characterized the hominoids. The presence of lateral and dorsal ponticles in humans appeared to correspond to their persistence within the progressive disappearance of the atlantal ponticles, constituting an evolutionary tendency characteristic of primates and particularly of hominoid evolution.

Posterolateral protrusion of the vertebral artery over the posterior arch of the atlas: quantitative anatomical study using three-dimensional computed tomography angiography

“…This osseous bridge has been called by various names in the literature: atlantic ponticulus, posterior ponticulus, bony ponticles over the groove for the VA, and posterior bridging of the atlas. 4,6,10,13,15,20 Previous studies of dry bones or cadavers have found osseous bridges in 5.0-34.66%. 10,13,15,17,20,23 On radiographic studies, the bridge was found in 11-15.6%.…”

“…4,6,10,13,15,20 Previous studies of dry bones or cadavers have found osseous bridges in 5.0-34.66%. 10,13,15,17,20,23 On radiographic studies, the bridge was found in 11-15.6%. 4,11,20,24 The incidence of osseous bridges in our study was lower than those in past reports, and it is difficult to explain the cause of this wide disparity.…”

Morphometry and Variations of Bony Ponticles of the Atlas Vertebrae (C1) in Kenyans

“…The atlas bridges are a shared structure between human and non-human primates. The posterior bridge is found dorsal to the lateral mass on the posterior arch of the atlas (Le Minor & Trost, 2004) and when complete, forms the retroarticular canal (Mitchell, 1998a(Mitchell, , 1998b) also called a Kimmerle's variant (Kimmerle, 1930) or arcuate foramen (Von Torklus & Gele, 1972). Lateral bridges, are less common than the posterior and may also exist as complete foramina (Mitchell, 1998a(Mitchell, , 1998b, called the supratransverse foramina (Chevrel et al, 1965 cited by Le Minor & Trost).…”

Ontogenetic change and geographical variation of atlas bridging in Japanese macaques (Macaca fuscata)

“…As for atlas bridging in extant nonhuman primates, there are only a few studies (Loth-Niemerycz, 1916;Sato and Noriyasu, 1978;Yamamoto and Kunimatsu, 2002a, b;Le Minor and Trost, 2004), most of which were based on analysis at the genus or family levels. These studies showed that prevalence of atlas bridges in humans is much lower than in the other primate taxa.…”

“…These studies showed that prevalence of atlas bridges in humans is much lower than in the other primate taxa. Le Minor and Trost (2004) studied atlas bridges in 41 genera of extant nonhuman primates and discussed possible evolutionary trends. In their study, however, the material lacked data such as age and sex, and, except for the hominoids, the data were analyzed at the generic level.…”