Shoulder

Brachium

Antebrachium

Facial and Masticatory Muscles

Thorax and Heart

Brain

Body Wall

Hip and Thigh

Shank and Foot

Digestive System

Urinary and Reproductive Systems

Hip and Tail

Body Wall Muscles of the Cat (Felis catus)

Photos and text by Adam Hartstone-Rose

Introduction:

The cat body wall is pretty typical of most mammalian forms in its muscular composition and the relationships of those muscles.  The ventral body wall is remarkably similar to that of the human, dominated by the overlapping layers of abdominal oblique and rectus muscles.  The dorsal body wall is slightly different than that of people in that the erector spinae muscles, long strap-like muscles that run close to and parallel to the vertebral column, are relatively longer and stronger in the cat.  The greater length is due to the fact that the lumbar region of the spine is relatively longer in the cat, and the greater strength is due to the quadrupedal stance and locomotion.  In humans, the erector spinae are mostly recruited to maintain the upright position of the torso and resist the force of gravity, whereas the cat needs them to maintain the arch of the back (like the horizontal supports of a suspension bridge) and to aid in locomotive propulsion. [1]

Dissection Technique:

Remove the skin overlying the area of interest.  To do this, lift the skin with forceps, and break the connective fascia using blunt dissection.  The skin overlying the areas discussed is very loosely connected and thus, this process is relatively easy.  Clean the remaining fascia off of the muscles to better see the separations between the muscles.

Abdominal Hypaxial Musculature:

Since the muscles of the ventral body wall are layered, the only way to see them all at the same time is to cut “windows” in the superficial layers to reveal sections of the deeper layers.  I recommend reflecting sections of the superficial most layers from one side of the animal and preserving them intact on the other.

Table 1.  Abdominal hypaxial musculature [2]. 

These muscles are all fairly thin in the cat and serve primarily to support the abdominal viscera [2].  They meet in the midline at the linea alba (literally “white line”).

Thoracic Hypaxial Musculature:

The thoracic hypaxial muscles are the muscles of the ribcage deep to many of the muscles of the shoulder girdle.  The three intercostal muscles, external intercostalis, internal intercostalis and innermost intercostalis are the equivalent of external abdominal oblique, internal abdominal oblique and transversus abdominis respectively, and their fibers follow in the same direction as those of their caudad equivalents.  They serve a small role in breathing, by lifting the ribcage craniad and, thus, expanding the chest volume [2].

Epaxial Musculature:

As noted in the introduction, the muscles that run along side and parallel to the spine in the cat are relatively powerful.  The most medial muscle that runs on either side of the spine is the spinalis.  Lateral to that is longissimus and further lateral is iliocostalis.  This is the same arrangement found all mammals, and like in humans, in cats all three of these muscles extend along the spine from the pelvic region all the way toward the head.  In the neck they differentiate and are given different names [2].  Deep to these muscles are shorter muscles that run between the vertebrae called multifidus spinae.

Table 2.  Epaxial Musculature.  Adapted from [1].

Discussion:

The muscles examined in this dissection are fairly easy to understand.  The muscles of the ventral abdomen run at a right angle with the external and internal abdominal obliques creating an “X” and the transversus and rectus abdominis making a “+.”  Because of this basket-like crosshatching, these thin muscles adequately support the viscera.

The epaxial musculature is simpler in orientation, but larger and more important in locomotion and for support.  All quadrupedal animals have to deal with the suspension bridge problem: the center of gravity of the animal is not directly supported from below but rather by column like supports (fore and hind limbs) which are spread toward the distal ends of the trunk.  Thus cats have strong erector spinae.  These muscles are also recruited for locomotion [1] in that animals are able to increase their stride length and overall propulsive force by strong flexible back extension and flexion.

References:

1. Walker, W. F. 1970. Vertebrate Dissection.  Philadelphia: W. B. Saunders Co.

2. Reighard, J. & Jennings H.S. 1935.  Anatomy of the Cat.  New York: Henry Holt and Co.