Testudines generally presents a considerable wealth of osteological elements of the skull that makes crucial the detailed knowledge of these bone structures, mainly in solving problems of classification and determination of species. Emydidae is an important group of chelonians, but the cranial anatomy knowledge is limited, mainly of the species of the genus Trachemys. The aim of the present study is to describe the osteology (in particular, the intraspecific variations) of the skull and mandible of T. dorbigni. 82 specimens of T. dorbigni from the Herpetological Collection of the Laboratory of Vertebrate Zoology/Institute of Biology/Universidade Federal de Pelotas were used in this study. The results indicated a set of characteristics not previously described for the specie’s skull, as well as several characteristics intraspecifically variable. Intraspecific variation was found in the pattern of jugal, frontal, prefrontal, vomer, quadratojugal and exoccipital bones, further the cases of absence and diversification in the position of the foramina praepalatinum and foramen nervi hypoglossi, and an observation of foramens that were not described in literature. Therefore, it is possible to state that there is considerable intraspecific variation in the Trachemys dorbigni’s skull, although it maintains general characteristics similar to other Emydidae’s species.

中文翻译：

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滑龟 Trachemys dorbigni (Testudines, Emydidae) 的头骨和下颌骨的形态学和种内变异

Testudines 通常提供了相当丰富的颅骨骨学元素，这些元素对于这些骨骼结构的详细知识至关重要，主要用于解决物种的分类和确定问题。Emydidae是龟类的一个重要群体，但颅骨解剖知识有限，主要是Trachemys属的物种。本研究的目的是描述 T. dorbigni 头骨和下颌骨的骨学（特别是种内变异）。在这项研究中使用了来自脊椎动物动物学实验室/生物学研究所/Universidade Federal de Pelotas 的爬虫学收藏的 82 份 T. dorbigni 标本。结果表明，该物种的头骨有一组以前没有描述过的特征，以及一些种内可变的特征。在颈骨、额骨、前额骨、犁骨、四颌骨和外枕骨的模式中发现了种内变异，此外还有前腭孔和舌下神经孔的位置缺失和多样化的情况，以及未描述的孔的观察文学。因此，可以说 Trachemys dorbigni 的头骨存在相当大的种内变异，尽管它保持与其他 Emydidae 物种相似的一般特征。