**Question:** Floor of posterior triangle of neck is formed by

A. Hyoid
B. Digastric muscle
C. Longus colli muscle
D. Longus capitis muscle

**Core Concept:** The posterior triangle of the neck is a region located in the posterior aspect of the neck, bounded superiorly by the posterior border of the sternocleidomastoid muscle, inferiorly by the clavicle, and laterally by the transverse cervical artery. The floor of this triangle is the lower part of the triangle, which contains important structures.

**Why the Correct Answer is Right:** The correct answer is formed by the longus capitis muscle. The posterior triangle of the neck is divided into three compartments: superior, middle, and inferior. The floor of the posterior triangle is the inferior compartment, which is formed by the longus capitis muscle. This muscle arises from the transverse processes of C1-C6 vertebrae and inserts into the atlantoaxial joint, helping to stabilize the atlantoaxial joint complex.

**Why Each Wrong Option is Incorrect:**

A. Hyoid: The hyoid is a ring-like bone that supports the tongue and forms part of the pharynx. It is not a muscle and contributes to the floor of the posterior triangle, but not as part of the inferior compartment.

B. Digastric muscle: The digastric muscle is the most medial muscle in the posterior triangle and is part of the inferior compartment. However, it is not the correct answer because it is not the primary structure forming the floor of the posterior triangle.

C. Longus colli muscle: The longus colli muscle is the most lateral muscle in the posterior triangle and is also part of the inferior compartment. However, it is not the correct answer because it is not the primary structure forming the floor of the posterior triangle.

**Clinical Pearls:**

1. Understanding the anatomy of the posterior triangle of the neck is essential for assessing and treating patients with neck pain and other disorders affecting this region.
2. The posterior triangle is a crucial area for clinical examination and palpation during a physical examination of the head and neck.
3. Knowledge of the posterior triangle's anatomy helps to identify and differentiate between various types of neck pain, such as referred pain from the upper thoracic spine or cervical spine.

For example, palpation of the longus colli muscle can help differentiate between costoclavicular joint pain and sternoclavicular joint pain, as both joints can cause referred pain to the posterior triangle. In cases of sternoclavicular joint pain, palpation of the longus colli muscle may elicit pain due to its close relationship with the sternoclavicular joint capsule. In cases of costoclavicular joint pain, palpation of the longus colli muscle may not elicit pain, as its origin is more distant from the costoclavicular joint compared to the sternoclavicular joint.