Deufel Alexandra, Cundall David
Department of Biology, Minot State University, Minot, North Dakota 58707, USA.
J Morphol. 2010 Jan;271(1):73-85. doi: 10.1002/jmor.10782.
Elapid snakes have previously been divided into two groups (palatine erectors and palatine draggers) based on the morphology and inferred movements of their palatine bone during prey transport (swallowing). We investigated the morphology and the functioning of the feeding apparatus of several palatine draggers (Acanthophis antarcticus, Oxyuranus scutellatus, Pseudechis australis) and compared them to published records of palatine erectors. We found that the palatine in draggers does not move as a straight extension of the pterygoid as originally proposed. The dragger palato-pterygoid joint flexes laterally with maxillary rotation when the mouth opens and the jaw apparatus is protracted and slightly ventrally during mouth closing. In contrast, in palatine erectors, the palato-pterygoid joint flexes ventrally during upper jaw protraction. In draggers, the anterior end of the palatine also projects rostrally during protraction, unlike the stability of the anterior end seen in erectors. Palatine draggers differ from palatine erectors in four structural features of the palatine and its relationships to surrounding elements. The function of the palato-pterygoid bar in both draggers and erectors can be explained by a typical colubroid muscle contraction pattern, which acts on a set of core characters shared among all derived snakes. Although palatine dragging elapids share a fundamental design of the palato-maxillary apparatus with all higher snakes, they provide yet another demonstration of minor structural modifications producing functional variants.
基于眼镜蛇科蛇类在捕食（吞咽）过程中上颚骨的形态及推测的运动方式，此前它们被分为两组（上颚竖起者和上颚拖动者）。我们研究了几种上颚拖动者（南极棘蛇、盾鳞棘背蛇、澳洲拟眼镜蛇）进食器官的形态及功能，并将其与已发表的上颚竖起者的记录进行比较。我们发现，拖动者的上颚并非如最初所提出的那样作为翼骨的直接延伸而移动。当嘴巴张开且颌部器官前伸时，拖动者的上颚 - 翼骨关节会随着上颌旋转而向侧面弯曲，在嘴巴闭合时则会稍微向下弯曲。相比之下，在上颚竖起者中，上颚 - 翼骨关节在上颌前伸时会向下弯曲。在拖动者中，上颚的前端在伸展时也会向前突出，这与竖起者中前端的稳定性不同。上颚拖动者在上颚及其与周围元素的关系的四个结构特征上与上颚竖起者不同。拖动者和竖起者的上颚 - 翼骨杆的功能都可以通过典型的游蛇科肌肉收缩模式来解释，这种模式作用于所有衍生蛇类共有的一组核心特征。尽管上颚拖动的眼镜蛇科蛇类与所有高等蛇类在上颚 - 上颌装置的基本设计上有共同之处，但它们再次证明了微小的结构改变会产生功能变体。
