Dissection of Rabbit trunk, BAA 289L 2004

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Body Wall Muscles of the Rabbit (Oryctolagus cuniculus)

Photos and text by Janelle Cooper and Alexandra Sardi

Dissection Notes:

We began this dissection by making a medial incision across the median plane and then an incision across the axial plane. The abdominal muscles of the rabbit are extremely thin and it was impossible not to cut into the abdominal cavity. Furthermore, it was extremely difficult to identify and separate the different muscle layers and we had to rely mostly on striations to do so. The thoracic muscles were a little bit larger and less difficult to separate but we still relied heavily on striations to tell them apart. We discovered the intercostal nerves, arteries and veins on the medial side of the ribs running along the sagittal plane. The hypaxial muscles lay superficial to them.

Discussion:

We began our dissection in the abdominal area. The most superficial muscle is the external oblique muscle, which covers the entire abdominal area, and the rectus abdominis, which runs along the medial line only. Medial to the external oblique is the internal oblique, which is present mostly caudally and is distinguishable due to the striations that run in the opposite direction. The muscles are extremely thin and interwoven and it is practically impossible to separate the two. The internal oblique of male rabbits loops around to form the cremaster muscle, which winds around the spermatic cord when contracted and retracts the testes into the canals. This will be further discussed in the reproductive system lab. The transversus abdominis is also very thin and is distinguishable because of its transverse striations. The external oblique, internal oblique and transversus muscles all developed from the parietal muscles, along with the external and internal intercostals muscles (1). Rabbits have little use for the oblique muscles in locomotion, as can be inferred from their size, but the intercostals serve as accessory muscles in respiration (1,2). The serratus dorsalis and scalenes, the supracostal muscles, assist the intercostals and also help support the abdominal viscera in a muscular sling along with the rectus, oblique and transversus muscles (1,3).

The intercostal muscles (external, internal and innermost) pass mostly obliquely from origin to insertion (3,4). The innermost intercostals fix the intercostal spaces during respiration, and the external and internal intercostals do the same and also help to elevate the ribs during respiration (3).

Muscle	Origin	Insertion	Action
External Oblique	caudal ribs and lumbodorsal fascia	linea alba of the abdomen	support abdominal viscera, constrict abdomen
Internal oblique	lumbodorsal fascia and inguinal ligament	linea alba of the abdomen	support abdominal viscera and constrict abdomen
Transversus abdominis	inner surface of caudal cartilage ribs, transverse processes of lumbar vertebrae, ilium and inguinal ligament	linea alba of the abdomen	support abdominal viscera, constrict abdomen
Rectus abdominis	tubercle of pubis	cartilage ribs	support abdominal viscera, maintain vertebral arch
External intercostals	vertebral half of ribs cranial to insertion	sternal half of ribs caudal to origin	draw ribs forward to expand the thoracic basket in respiration
Internal intercostals	sternal half of ribs cranial to insertion	vertebral half of ribs caudal to insertion	draw ribs forward to expand the thoracic basket during respiration
Innermost intercostals	inferior border of ribs	superior border of ribs	elevates ribs
Serratus dorsalis cranialis	lumbodorsal fascia covering the spinalis muscles	first nine ribs	draws ribs forward
Serratus dorsalis caudalis	lumbodorsal fascia covering longissimus lumborum	last four ribs	draws ribs forward
Scalenes	ribs	transverse processes of cervical vertebrae	flex the spinal column and aid in respiration
Multifidus spinae	lamina and mammillary processes of the sacral, lumbar and dorsal transverse processes of the thoracic vertebrae	fibers pass forward over first two vertebrae and insert on neural spine of third vertebra forward from origin	extends vertebral column
Semispinalis thoracis	lumbodorsal fascia covering longissimus lumborum	spinous processes of cranial thoracic vertebrae	extends vertebral column
Semispinalis cervicis	spinous processes of thoracic vertebrae	spinous processes of all except cervical vertebrae except atlas	extends neck
Semispinalis capitis (biventer cervicis and complexus)	transverse processes of cervical and thoracic vertebrae	spinous processes of cervical vertebrae and occipital bone	extends vertebral column and head
Longissimus lumborum	iliac crest and articular process of lumbar vertebrae	mammillary and accessory processes of lumbar vertebrae	extends lumbar vertebrae
Longissimus thoracis	mammillary and spinous processes of lumbar vertebrae	accessory processes of thoracic vertebrae and ribs	extends thoracic vertebrae
Longissimus cervicis	transverse and articular processes of thoracic vertebrae	transverse processes of cervical vertebrae	extends cervical vertebrae
Longissimus capitis	articular processes of last four cervical vertebrae	mastoid process of temporal bone	turns head laterally
Iliocostalis	ilium, deep lumbar fascia, transverse processes of lumbar vertebrae	ribs and transverse processes of lumbar vertebrae cranial to origin	draws ribs caudally
Splenius capitis	nuchal ligament from first two thoracic vertebrae beneath fascia of origin of serratus dorsalis cranialis.	lateral surface of occipital bone and atlas	raises and turns head laterally

Adapted from [3].

References:

1. Kemtn, George C., Carr, Robert K., Comparative Anatomy of the Vertebrates, McGraw Hill, New York, 2001.

2. Kardong, Kenneth V., Vertebrates: Comparative Anatomy, Function, Evolution. McGraw Hill, New York: 2002.

3. McLaughlin C.A., Chiasson R.B., Laboratory Anatomy of the Rabbit, McGraw-Hill, New York: 1990.

4. Popesko, P., Rajtova V., Horak J., A Coulour Atlas of Anatomy of Small Laboratory Animals, V1. Wolfe Publishing Ltd. London, England: 1992.

Artwork: Weil, from Stubbs' 1776 "Anatomy of the Horse."
Background free from Eos Development, with slight color modification.