Morphological, Physiological, and Behavioral Studies of the Facial Musculature of the Coati <i>(Nasua)</i>; pp. 104–115

Abstract

The muscles and motor nerves which contribute to the complex facial behavior of the coati <i>(Nasua) </i>have been investigated with techniques from various disciplines. (1) Anatomical techniques included gross dissection of embalmed and fresh heads, and microscopic examination of stained serial sections of the proboscis. The origin, insertion, relative size and shape of each of the facial muscles, and the general topography of the facial nerve from the stylomastoid foramen to its muscles were determined and represented by line drawings. (2) Physiological techniques incorporated monopolar electrical stimulation of individual branches of the facial nerve with simultaneous recording of the resulting movement on movie film. This procedure verified the innervation of a muscle by a particular nerve branch and displayed the action each muscle has on the moveable structures of the head (e.g., proboscis, vibrissae, pinnae, or lips). (3) Behavioral techniques involved analysis of microbehaviors, as recorded by high-speed movies, with respect to the coordinated activity of several individual muscles.The extrinsic and intrinsic muscles of the proboscis were found to be numerous, anatomically complex, and capable of producing a variety of different movements. These morphological specializations correspond to the behavioral data which illustrate the coati's unusual propensity for delicate and intricate microbehaviors involving the proboscis.The relevance of this investigation is discussed in terms of a five-step program for the analysis of the anatomical and physiological features of motor systems responsible for overt behavior. The sequence of steps is as follows: (1) selection of microbehaviors; (2) detailed study of muscles underlying microbehaviors; (3) correlation of muscular activity with microbehaviors; (4) determination of the musculotopic organization of &#913;-motor neurons; and (5) search for central motor circuits and correlation of higher neural activity with microbehaviors.