3D Analysis of Primate Neck Anatomy using Contrast‐Enhanced CT Imaging, Fascicle‐Tracking Algorithms, and Muscle Mechanics

The functional anatomy of the neck is a major component of an animal's postural and locomotor repertoire, yet remains poorly understood in part due to the anatomical complexity of the cervical musculoskeletal system. Here we use a new methodology to visualize and quantify aspects of muscle architecture, as well as to explore 3D muscle mechanics of the head and neck of a Philippine tarsier ( Carlito syrichta ). First, the specimen was contrast stained and microCT‐scanned (0.043mm 3 voxels). From these data, individual neck muscles were segmented using Avizo software. We tracked individual muscle fascicles based on grayscale values and fascicle diameter in Avizo Xfiber. Outputs from Xfiber (fascicle length, pennation angle, and muscle volume) were used to calculate estimates of physiological cross‐sectional area (PCSA) in the intrinsic epaxial neck muscles. We combined PCSA values with resultant muscle force vectors to estimate muscle moments about joints for flexion, extension, lateral flexion and rotation about each cervical intervertebral joint. Results demonstrate that the moment arms for muscles used in head and neck rotation like obliquus capitis inferior are larger in the tarsier relative to body size when compared to humans. This implies that an increase in rotational movements in this species is accomplished by modifying lines of action instead of increasing muscle force. This workflow provides a more comprehensive characterization of musculoskeletal functional capacity in a complex system. Not only does it provide novel insight into the neck of this unusual primate, but provides the basis to compare primates with different positional behaviors. This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .