title: Evolutionary transformation of the cervicobrachial plexus in the colugo (Cynocephalidae: Dermoptera) with a comparison to treeshrews (Tupaiidae: Scandentia) and strepsirrhines (Strepsirrhini: Primates).
abstract: Four cervicobrachial plexuses from two colugos (Dermoptera), which are gliding  mammals with semi-elongated necks, were dissected with imaging analysis  and compared with those in its relatives, 12 sides of six treeshrews (Scandentia)  and 32 sides of 16 strepsirrhines (Primates), for considering of its evolutionary  constraint and functional adaptation. (1) The relative cervical length in the  colugos was significantly longer than those in the others, regardless of the  number and proportion of vertebrae. (2) In all examined colugos, the cervical  plexus exhibited broader cervical root segments comprising the hypoglossal  (N. XII) and first to fifth cervical (C1-C5) nerves, whereas the brachial plexus  exhibited concentrated segments comprising C6 to the first thoracic nerve (T1)  and part of T2. (3) On the other hand, the cervical plexus composed of N. XII  and C1-C4 and the brachial plexus composed of C5-T1(2) were formed in all  treeshrews (12/12 sides, 100.0%) and most strepsirrhines (27/32 sides, 84.4%)  as seen in most terrestrial placental mammals. (4) Similar root segments of  broader cervical and concentrated brachial plexuses were found in five sides of  three strepsirrhines (15.6%), which are species with somewhat longer necks  than the other strepsirrhines and treeshrews. Based on present and previous  reports on elongated and shortened neck mammals, the modified root segments  of the cervicobrachial plexus in the colugo appears to be related more  to neck length than to its ecological habit, specialized locomotion, or any phylogenetic  constraint.
authors.affiliation: Department of Anatomy, Toho University, Tokyo, Japan. tomokazu.kawashima@med.toho-u.ac.jp
authors.forename: T
authors.initials: T
authors.lastname: Kawashima
authors.forename: K
authors.initials: K
authors.lastname: Murakami
authors.forename: M
authors.initials: M
authors.lastname: Takayanagi
authors.forename: F
authors.initials: F
authors.lastname: Sato
mesh_terms: D000818:Animals; D005075:Biological Evolution; D001917:Brachial Plexus / Q000033:anatomy & histology* / Q000000981:diagnostic imaging; D007900:Lemur / Q000033:anatomy & histology*; D009333:Neck / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D010802:Phylogeny; D013045:Species Specificity; D013126:Spinal Nerve Roots / Q000033:anatomy & histology / Q000000981:diagnostic imaging; D011443:Strepsirhini / Q000033:anatomy & histology*; D014057:Tomography, X-Ray Computed; D014418:Tupaiidae / Q000033:anatomy & histology*