4.8: Directional Terms
Diagram 4.16 : The directional terms used with animals
Diagram 4.17 : Transverse and longitudinal sections of a mouse
In the following chapters the systems of the body in the list above will be covered one by one. For each one the structure of the organs involved will be described and the way they function will be explained.
In order to describe structures in the body of an animal it is necessary to have a system for describing the position of parts of the body in relation to other parts. For example it may be necessary to describe the position of the liver in relation to the diaphragm, or the heart in relation to the lungs. Certainly if you work further with animals, in a veterinary clinic for example, it will be necessary to be able to accurately describe the position of an injury. The terms used for this are called directional terms .
The most common directional terms are right and left . However, even these are not completely straightforward especially when looking at diagrams of animals. The convention is to show the left side of the animal or organ on the right side of the page. This is the view you would get looking down on an animal lying on its back during surgery or in a post-mortem. Sometimes it is useful to imagine ‘getting inside’ the animal (so to speak) to check which side is which. The other common and useful directional terms are listed below and shown in diagram 4.16.
| Term | Definition | Example |
|---|---|---|
| Dorsal | Nearer the back of the animal than | The backbone is dorsal to the belly |
| Ventral | Nearer the belly of the animal than | The breastbone is ventral to the heart |
| Cranial (or anterior) | Nearer to the skull than | The diaphragm is cranial to the stomach |
| Caudal (or posterior) | Nearer to the tail than | The ribs are caudal to the neck |
| Proximal | Closer to the body than (only used for structures on limbs) | The shoulder is proximal to the elbow |
| Distal | Further from the body than (only used for structures on limbs) | The ankle is distal to the knee |
| Medial | Nearer to the midline than | The bladder is medial to the hips |
| Lateral | Further from the midline than | The ribs are lateral to the lungs |
| Rostral | Towards the muzzle | There are more grey hairs in the rostral part of the head |
| Palmar | The "walking" surface of the front paw | There is a small cut on the left palmar surface |
| Plantar | The "walking" surface of the hind paw | The pads are on the plantar side of the foot |
Note that we don’t use the terms superior and inferior for animals. They are only used to describe the position of structures in the human body (and possibly apes) where the upright posture means some structures are above or superior to others.
In order to look at the structure of some of the parts or organs of the body it may be necessary to cut them open or even make thin slices of them that they can be examined under the microscope. The direction and position of slices or sections through an animal’s body have their own terminology.
If an animal or organ is sliced lengthwise this section is called a longitudinal or sagittal section . This is sometimes abbreviated to LS.
If the section is sliced crosswise it is called a transverse or cross section . This is sometimes abbreviated to TS or XS (see diagram 4.17).