Chapter 7 Myology of the Thorax and Abdomen PDF

CHAPTER 7 MYOLOGY OF THE THORAX AND ABDOMEN COMPILED BY PROF CROLE  EPIAXIAL MUSCLES The epiaxial musculature associated with the vertebra...

CHAPTER 7 MYOLOGY OF THE THORAX AND ABDOMEN COMPILED BY PROF CROLE  EPIAXIAL MUSCLES The epiaxial musculature associated with the vertebral column and ribs may be divided into three longitudinal muscle masses on each side. Each is composed of many overlapping fascicles. These three columns include the lateral iliocostalis system, the intermediate longissimus system and the medial spinalis et semispinalis system. Various fusions occur between these columns, giving rise to different muscle patterns. These muscles act as powerful extensors of the vertebral column and also produce lateral movement of the trunk when contracting unilaterally. In the neck region the M. iliocostalis is absent and the M. splenius lies laterally to the other two groups.  The splenius muscle lies on the dorsolateral aspect of the neck, deep to the rhomboid muscle. Origin: The spinous processes of the first 3 thoracic vertebrae as well as from the median raphe of the neck. Insertion: The mastoid process and the back of the skull. 1 2 3 mastoid process  It is divided into lumbar and thoracic parts. Origin: The wing of the ilium and ribs. Insertion: The transverse processes of the lumbar, thoracic and last cervical vertebrae.  The muscle is divided into lumbar, thoracic, cervical and capital parts. Origin: The wing of the ilium and from the spinous processes of the vertebrae Insertion: The transverse processes of the vertebrae, as well as on the back of the head.  The muscle consists of thoracic, cervical and capital parts. Origin: The transverse and articular processes of the thoracic and cervical vertebrae. Insertion: They pass craniodorsally and insert on the spinous processes of the thoracic and cervical vertebrae, as well as on the back of the head.  The nuchal ligament extends from the tip of the spinous process of the first thoracic vertebra to the caudal end of the spine of the axis. It is a laterally compressed, paired, yellow band of elastic connective tissue.  The fibres of the external intercostal muscles pass caudoventrally from the caudal border of one rib to the cranial border of the rib behind. Collectively they pull the ribs cranially and laterally, thereby enlarging the thoracic cavity during inspiration. The fibres of the internal intercostal muscles pass cranioventrally (at right angles to those of the external muscles) from the caudal border of one rib to the cranial border of the rib behind it. They pull the rips caudally and medially, thereby compressing the thorax during expiration.  ABDOMINAL MUSCLES The abdominal muscles are broad, flat muscles with extensive aponeuroses which close the gap between the rib cage, lumbar vertebrae and pelvis. They are arranged in four layers with four different fibre directions.  M. obliquus externus abdominis The external oblique abdominal muscle is the most superficial of the abdominal muscles. Origin: The ribs, interdigitating with those of the serratus ventralis muscle and run in a caudoventral direction. Insertion: Tuber coxae, shaft of the ilium, Linea alba, prepubic tendon. Linea alba External opening of the inguinal canal M. obliquus internus abdominis The internal oblique abdominal muscle is triangular in shape. Origin: Tuber coxae; the fibres run cranioventrally Insertion: Linea alba and the inner surface of the ribs. Linea alba M. transversus abdominis This is the deepest of the abdominal muscles. Origin: Its fibres run transversely, from the transverse processes of the lumbar vertebrae and the medial aspect of the asternal ribs Insertion: Linea alba. Linea alba  M. rectus abdominis The rectus abdominis is the most ventral of the abdominal muscles. Its fibres run in a craniocaudal direction. Origin: The xiphoid cartilage, sternum and costal arch of the ribs Insertion: The prepubic tendon (and therefore on the pubis). prepubic costal arch tendon pubis sternum xiphoid cartilage Note that the muscle fibres are interrupted by transverse bands of connective tissue, dividing the muscle into blocks of muscular tissue. The medial borders of the left and right rectus abdominis muscles are attached to each other by a strong band of fibrous connective tissue, forming a distinct white line, the Linea alba, on the ventral midline of the abdomen.  INGUINAL CANAL The inguinal canal is a slit-like space between the external and internal oblique abdominal muscles. The inner or deep opening to the canal is formed by the and the aponeurosis of the.  INGUINAL CANAL The external or superficial opening of the canal is a slit in the aponeurosis of the external oblique abdominal muscle.  INGUINAL CANAL The canal gives passage to the spermatic cord in the male and to bloodvessels in the female animal.