# An Unreported Variant of the Rhomboideus Muscle With an Additional Cervical Origin in a Cross‐Breed Dog Cadaver

## TL;DR

A new muscle variant in a dog cadaver shows an unusual cervical origin and nerve supply, offering insights into carnivore anatomy and evolution.

## Contribution

The discovery of an unreported rhomboideus muscle variant with a cervical origin in a dog cadaver.

## Key findings

- A ribbon-shaped muscle slip originated from the second cervical vertebra's transverse process in a dog cadaver.
- The slip was innervated by cervical spinal nerve ventral branches, distinct from neighboring muscles.
- This anatomical variant has not been previously documented in canines.

## Abstract

The m. rhomboideus of domestic dogs typically originates from the dorsal median raphe of the neck and cranial thorax, with a distinct slip from the occiput, and is composed of the three parts: cervicis, thoracis and capitis. Here, an additional muscular slip was identified on the left side of an adult male cross‐breed dog cadaver. This ribbon‐shaped slip arose indirectly via tendinous fibres from the transverse process of the second cervical vertebra and extended caudodorsally to join the capital part near its scapular insertion. The slip was innervated by ventral branches of the cervical spinal nerves, consistent with the usual supply of the rhomboideus complex and distinct from the neighbouring m. serratus ventralis cervicis, despite their segmental overlap. Such a variant of the m. rhomboideus has not been previously reported in dogs. Recognition of incidental muscular variations, particularly with regard to their innervation patterns, provides insights into embryologic development and phylogenetic relationships in carnivores.

A distinct muscular slip (arrows) was observed in the cervical region of a dog. It originated from the transverse process of the axis and joined the rhomboideus capitis (RCa) near its scapular insertion. The slip was innervated by a branch of the cervical ventral rami. This variant provides insights into anatomical variation and comparative morphology.