Body Cavities and Thoracic Anatomy

Study Notes

The cephalic cavity is located in the head and includes the cranial cavity (brain), oral cavity, and nasal cavity.
The coelomic cavity is located in the trunk and includes the thoracic cavity, abdominal cavity, and pelvic cavity.
The thoracic cavity is smaller than the thoracic cage and is separated from the abdominal cavity by the diaphragm.
The abdominal cavity is separated from the pelvic cavity by the linea terminalis.

The thoracic cavity is the second largest cavity in the body.
It is bounded dorsally by the thoracic vertebrae, caudally by the diaphragm, and laterally by the ribs and intercostal muscles.
The thoracic inlet is a small, narrow, oval opening located in the most cranial portion of the thoracic cavity.
The thoracic outlet is located in the most caudal portion of the thoracic cavity.

Ribs are classified into sternal (true), asternal (false), and floating ribs.
Sternal ribs are the most cranial group of ribs and their cartilages directly join the sternum.
Anteral ribs are located caudal to the sternal ribs, and their costal cartilages merge to form the costal arch, which indirectly joins them to the sternum.
Floating ribs are located at the caudal end of the rib series and do not join the sternum or the costal arch.

The abdominal cavity extends from the diaphragm to the pelvic inlet.
It is divided into the intra-thoracic part of the abdominal cavity (most cranial part) and the fleshy part (flank region).
The cranial part of the abdominal cavity is bounded dorsally by lumbar vertebrae, ventrally by the xiphoid cartilage, and laterally by ribs.
The fleshy part of the abdominal cavity is bounded by the abdominal wall and its muscles.
The abdominal region can be divided into three main regions by two transverse imaginary lines:
- Cranial plane: passes through the last rib.
- Caudal plane: passes through the tuber coxae.

The cranial abdominal region (epigastric) extends from the diaphragm to the cranial plane.
The middle abdominal region (mesogastric) extends from the cranial plane to the caudal plane.
The caudal abdominal region (hypogastric) extends from the caudal plane to the pelvic inlet.
Each of these regions is subdivided into three further subregions by two para median planes.

Cutaneus tranki: a large muscle layer that covers the trunk wall and tenses and twitches the skin.
Tunica flava abdominalis: a sheet of elastic tissue that assists the muscles in supporting the abdominal viscera.
Linea alba: a median fibro-tendinous cord that extends from the xiphoid cartilage to the perpubic tendon.

The abdominal muscles are flat muscles composed of fleshy and aponeurotic parts.
They include:
- External oblique abdominal muscle
- Internal oblique abdominal muscle
- Transverses abdominis muscle
- Rectus abdominis muscle

Orifices of the diaphragm:
- Aortic hiatus: passage for the aorta.
- Esophageal hiatus: passage for the esophagus.
- Caval hiatus: passage for the caudal vena cava.
Umbilical opening: present in the fetus, it undergoes fibrosis and forms the umbilicus after birth.
Lumbo-costal arch: a slit-like passage between the ribs and sub-lumbar muscles that allows passage for the sympathetic nerve chain and splanchnic nerves.
Two openings of the fallopian tubes in females.
Two orifices of the inguinal canal.

The largest serous membrane in the body that lines the organs contained in the abdominal and pelvic cavities.
The peritoneum is divided into parietal and visceral peritoneum.
The parietal peritoneum lines the wall of the body cavity and is loosely attached.
The visceral peritoneum covers the visceral organs and is closely attached.
The connecting peritoneum is a double layer of serous membrane that connects the parietal layer to the visceral layer.
Types of connecting peritoneum:
- Omentum: folds attached to the stomach.
  - Greater omentum
  - Lesser omentum
- Mesentery: folds of peritoneum that suspend the intestinal tract from the dorsal wall of the abdomen.
- Ligament: folds of peritoneum that pass between viscera other than parts of the digestive tube or connect them to the abdominal wall.

Organs located behind the parietal peritoneum.
Include the caudal part of the urinary bladder, caudal part of the rectum, and two kidneys.

The smallest and most caudal body cavity.
Bounded dorsally by the sacrum, laterally by the ilium, and ventrally by the pubis and ischium.
The pelvic inlet is bounded dorsally by the first vertebra of the sacrum, ventrally by the pubis, and laterally by the ilio-pectineal line.
The pelvic outlet is bounded dorsally by the third vertebra of the coccygeal vertebrae, ventrally by the ischial arch.