Largest purely endocrine gland in the body.

A. Flat: Flat bones are thin, flattened, and often slightly curved, providing broad surfaces for muscle attachment and protection of vital organs. Examples include the sternum, ribs, scapulae, and cranial bones, which protect the brain and thoracic organs. Their structure consists of two layers of compact bone enclosing spongy bone (diploë).

B. Irregular: Irregular bones have complex shapes that do not fit into other bone categories. They often provide protection of nervous tissue and serve as multiple muscle attachment sites, such as the vertebrae, sphenoid, and facial bones. Their anatomy reflects specialized functions rather than uniform shape.

C. Short: Short bones are roughly cube-shaped and consist primarily of spongy bone with a thin outer layer of compact bone. They provide stability and support with limited movement, as seen in the carpals and tarsals of the wrist and ankle.

D. Regular: “Regular” is not a recognized anatomical classification of bone. Standard bone classifications include long, short, flat, irregular, and sesamoid bones.

A. Cervical sympathetic trunk: This is the superior portion of the sympathetic trunk in the cervical or upper thoracic region, far from the pelvic cavity. It provides sympathetic innervation to the head, neck, and upper thoracic viscera, such as the heart and lungs, through the cervical and superior thoracic paravertebral ganglia.

B. Thoracic sympathetic trunk: The thoracic sympathetic trunk runs parallel to the vertebral column within the chest cavity and gives rise to the splanchnic nerves. These nerves primarily target the prevertebral ganglia in the abdomen to regulate the function of the foregut and midgut, rather than descending into the true pelvis.

C. Lumbar sympathetic trunk: The lumbar sympathetic trunk is situated along the lumbar vertebrae and responsible for providing postganglionic fibers to the lower abdominal region and lower extremities. While it is continuous with the pelvic portion, it is anatomically distinct and superior to the sacral/pelvic region of the autonomic chain.

D. Abdominal prevertebral plexus: This points to the abdominal prevertebral plexus (specifically near the aortic bifurcation), which integrates both sympathetic and parasympathetic fibers. While these plexuses contribute to the pelvic viscera, they are located anterior to the great vessels and do not constitute the paravertebral "trunk" or chain itself.

E. Pelvic (sacral) sympathetic trunk: This identifies the pelvic (sacral) sympathetic trunk, which consists of the paravertebral ganglia located medial to the sacral foramina. These ganglia represent the terminal inferior portion of the sympathetic chain, where the two trunks converge at the coccyx to form the ganglion impar, providing sympathetic outflow to the pelvic organs and perineum.