Young B A, Sheft S, Yost W
Parmly Hearing Institute, Loyola University Chicago, Illinois 60626, USA.
J Exp Zool. 1995 Dec 15;273(6):472-81. doi: 10.1002/jez.1402730604.
The pine, gopher, or bull snake (Pituophis melanoleucus) makes two different defensive sounds. Hisses are characterized by lack of frequency and amplitude modulation; bellows have a brief initial period of high-amplitude, broad-frequency sound followed by a longer period of lower-amplitude, constant-frequency sound. Both defensive sounds contain distinct harmonic elements. The modulation and harmonic nature of these sounds seems to be unique among snakes. The larynx of Pituophis is unusual in having an epiglottal keel, a dorsal expansion of the cricoid cartilage, previously proposed to contribute to sound production; however, this study shows that it plays only a small role in increasing the amplitude of bellows. Within the larynx of Pituophis is a "vocal cord," the laryngeal septum, which is a flexible, horizontal shelf of tissue that divides the anterior portion of the larynx. Removal of the laryngeal septum alters the defensive sounds and eliminates their harmonic elements. The laryngeal septum is unique among previously described vertebrate vocal cords or folds because it is supported by the cricoid (as opposed to arytenoid) cartilage and is a single (as opposed to bilaterally paired) structure.
松树蛇、囊鼠蛇或牛蛇（Pituophis melanoleucus）会发出两种不同的防御性声音。嘶嘶声的特点是缺乏频率和振幅调制；吼声则是在短暂的初始阶段发出高振幅、宽频率的声音，随后是较长时间的低振幅、恒定频率的声音。两种防御性声音都包含独特的谐波元素。这些声音的调制方式和谐波性质在蛇类中似乎是独一无二的。牛蛇的喉部不同寻常，具有会厌嵴，即环状软骨的背侧扩张，此前有人认为这有助于发声；然而，这项研究表明，它在增加吼声的振幅方面只起很小的作用。在牛蛇的喉部有一个“声带”，即喉中隔，它是一块灵活的水平组织架，将喉部的前部隔开。切除喉中隔会改变防御性声音并消除其谐波元素。喉中隔在先前描述的脊椎动物声带或褶皱中是独一无二的，因为它由环状软骨（而非杓状软骨）支撑，并且是单一结构（而非双侧成对结构）。
