Practical Anatomy

The human body dissected, 2nd Edition

Jules Kieser, John Allan, Erin Hutchinson, Jason Hemingway, Desiré Brits, Erin Hutchinson, Jason Hemingway, Desiré Brits

• Publisher: Wits University Press
• Year: 2020
• ISBN:
  9781776145744
• Edition: 2
• Topic: Medicine
• Subtopic: Anatomy

Practical Anatomy is designed to enable novice anatomists to grasp the biological background of the human anatomy while understanding its complexity within the clinical context. As a guide to the dissection of the human cadaver, it provides an account of the biological and systemic foundations of the human body.In keeping with the tradition of its predecessor this revised edition is primarily aimed at undergraduate allied health sciences and medical students who are encountering dissection for the first time and are intimidated by the volume of information to be understood. In addition, some dissections of more complex regions of the anatomy have been integrated into the text for more advanced students.This version has built on the solid foundation of the first edition of Practical Anatomy and Man's Anatomy, incorporating all the features unique to these texts while updating the methodology and including the latest anatomical terminology as outlined in the Terminologia Anatomica. The text and illustrations have been simplified to provide a clear, concise and accessible dissection guide.

Chapter One

Introduction

The word ‘anatomy’ is derived from two Greek words, ana- and -tome, which, put together, mean ‘to cut up’. While this is its strict meaning, it has gradually become synonymous with ‘structure’. In the medical and allied fields, there are various ways in which ‘structure’ may be used or interpreted:

• clinical anatomy is used in diagnosis or treatment;
• surgical anatomy is used by the surgeon in the operating room;
• radiological anatomy is used by the radiologist in the interpretation of various image modalities, such as X-rays;
• comparative anatomy is used when comparing the structure of various animals;
• developmental anatomy is used to describe how the human body develops and grows.

All these terms only consider the ‘gross’ aspect of structures, that which can be seen by the naked eye. However, all gross structures are made up of smaller structures called tissues, the intricate composition of which is visible only under a microscope. The study of tissues under the microscope is called histology. Tissues, in turn, are made up of smaller elements, cells, the study of which is called cytology. The matter may be taken even further because cells are made up of chemical substances which consist of molecules which are made up of atoms. Collectively, cells, tissues and organs give form to the human body.

From the abovementioned, it is obvious that structure is basic to all physical things and function will depend to a large extent upon the nature of the structure. For the study of medicine and its allied sciences, a knowledge of structure is therefore a fundamental requirement. It is only through an understanding of the normal structure that an appreciation of the abnormal anatomy, pathology, is gained.

An understanding of anatomy is attained by studying the human body on a cadaver (preserved dead body). The first purpose will be to acquire knowledge of the shape and parts of the body together with the positions and relationships of the various organs within the body. The second and equally important purpose is to learn how to apply this knowledge to the living subject, since it is with living people that the doctor and allied practitioners are mostly concerned. Before this can be done, the technique of exposing the structures of the body must be acquired. This is called dissection.

Before commencing dissection of the body there are a number of things to be considered. The cadaver will have been preserved (embalmed) by the injection of preserving fluid containing, amongst other substances, alcohol, formaldehyde, phenol, glycerine and an antifungal agent. This solution kills most bacteria and viruses and thus it is unlikely that you will acquire any illness from handling such cadaveric material. There are, however, two hazards of which you should be aware.

The first is that some people are sensitive (allergic) to formaldehyde and should consult with their relevant department(s) and a medical practitioner. The second is that the chemical fumes arising from the cadaver have a tendency to affect some contact lenses. Wearers of contact lenses are therefore advised to wear glasses during dissection sessions.

During dissection it is mandatory to wear suitable clothing. A clean white coat or scrubs are protective and also lend an air of professionalism and dedication to the process of dissection of the human body, upon which it is your privilege to be educated. It is important to wear closed shoes as a falling scalpel may seriously injure a dissector’s foot. Gloves should also be worn during dissection and hands washed thoroughly after each session.

1.1 DISSECTION EQUIPMENT

A set of dissecting instruments is necessary to perform a dissection adequately and mainly include:

• a scalpel;
• two pairs of forceps;
• a pair of scissors;
• a probe;
• a sponge.

1.2 TERMINOLOGY

It is imperative to familiarise yourself with the names of the various organs and parts of the body. Most of the words in anatomy have been derived from Latin or Greek. A consideration of the parts will usually indicate the meaning of the word and will also give an indication of the function, location or shape of the structure. For example, the sternocleidomastoid muscle should be broken up into ‘sterno’, meaning sternum, ‘cleido’, meaning clavicle, and ‘mastoid’ referring to the mastoid process of the cranium; the full meaning of the term, therefore, is a muscle connecting the sternum and clavicle to the mastoid process.

In anatomy, the ‘anatomical position’ is the position of the whole body in space. In this position, the body is upright, facing forward, with the upper limbs at the sides, palms facing forward, the lower limbs together and the soles facing downwards. In this position, it is easy to see that the front of the body is called ‘anterior’, the back of the body is called ‘posterior’ and the sides of the body are called ‘lateral’. A part above another is called ‘superior’ and a part below another is called ‘inferior’. The positions of organs and structures within the body are related to the three planes or spaces (Fig. 1.1):

• A vertical cut from anterior to posterior divides the body into right and left sides and the plane is known as the ‘sagittal plane’. If the cut is in the midline of the body, the plane is known as the ‘median sagittal plane’, as the ‘median’ would divide the body into two equal halves. If the cut is parallel to the median sagittal plane, the plane produced is known as a ‘parasagittal plane’.
• A vertical cut from one side to the other divides the body into anterior and posterior sections and the plane produced is known as a ‘frontal’ or ‘coronal plane’.
• A horizontal cut across the body, parallel to the floor, divides the body into superior and inferior parts and the plane is known as a ‘transverse’ or ‘horizontal plane’.

Figure 1.1 Illustration of the anatomical terminology related to direction and planes of the body

These planes are all at right angles to one another. To understand more clearly how the position of a structure is described, examine the drawing of a transverse section through the chest (Fig. 1.2); place a marker anywhere within the diagram. Any structure in front of the marker is anterior (A) to it; any structure behind the marker is posterior (P) to it; any structure to the inner side of the marker is medial (M) to it and any structure to the outside of it is lateral (L) to it. A structure above another is superior to it, while a structure below another is inferior to it. It is also possible to describe combinations of positions such as anterolateral or posterosuperior. In breaking the first term up into component parts, we have antero- meaning towards the front and -lateral meaning towards the side. In geographical terms, this would be equivalent to the use of compounded directional names, such as southeast or southwest.

Figure 1.2 Descriptive terminology for anatomical position

In the case of the limbs and neurovascular structures, the same basic relationships apply, but as they have an origin, the terms ‘proximal’ and ‘distal’ replace the terms ‘superior’ and ‘inferior’ to describe the position of the structure in relation to its proximity to the origin.

In addition, in many textbooks and in specific regions of the body the terms ‘anterior’ and ‘posterior’ are often replaced by ‘ventral’ and ‘dorsal’. These terms are derived from the zoological terminology (venter = stomach; dorsum = back). The anterior surface of the hand is referred to as the ‘palmar surface’, and the sole of the foot the ‘plantar surface’. There are also words to denote depth. In describing depth, we use the terms ‘superficial’ and ‘deep’.

Regardless of the actual position of the body, for descriptive purposes the position of a specific structure must be translated into the anatomical position as described above. A common problem with beginners is that they have difficulty in this translation. With the body in supine position (lying upon its back), its anterior surface (the true front) is facing upwards and it is easy to misalign a structure by using ‘lying down’ terminology instead of the ‘upright’ anatomical terminology. This requires some practice and the best way to acquire the ability is by usage.

A further point in terminology is related to the movement of joints. When a joint bends in a sagittal plane so that the parts approach each other, this is called ‘flexion’. Thus, in flexion of the elbow, the forearm approaches the arm. When a joint bends from a position of flexion, so that its parts tend to straighten, this is called ‘extension’.

In the lower limb, the hip joint will flex anteriorly, whereas the knee joint will flex posteriorly. The foot is positioned at a right angle to the leg and, therefore, the ankle joint, in undergoing extension, will cause the foot to move superiorly, and when undergoing flexion will cause the foot to move inferiorly. These superior and inferior movements of the foot may also be referred to as ‘dorsiflexion’ and ‘plantar flexion’, respectively. When the sole of the foot is tilted laterally (outwards) or medially (inwards) these actions are called ‘eversion’ and ‘inversion’, respectively.

Rotation of a part may take place inwards, termed ‘internal’ or ‘medial rotation’, or outwards, ‘external’ or ‘lateral rotation’. Rotation of the hand and foot is named by the position to which the structure is moving, either toward a prone position, and thus the movement is called ‘pronation’, or a supine position, and the rotation is thus called ‘supination’.

Any action in which a part moves away from the sagittal plane is called ‘abduction’; an action that causes a part to move towards the sagittal plane is called ‘adduction’. A combination of the movements of flexion, abduction, extension and adduction is called ‘circumduction’ (moving in a circle); this may be seen at the wrist, shoulder, hip and foot joints.

Finally, with reference to terminology, students are constantly harassed by words combined with prefixes and suffixes. Anatomical terms with prefixes and suffixes are in very common use and it is advisable for the student to become wholly familiar with them. Students are therefore referred to the Terminologia Anatomica which can be found on the International Federation of Anatomical Associations (IFAA) website.

1.3 TECHNIQUES OF DISSECTION

A good dissection is like a work of art; the more often one looks at it, the more one sees in it. Like the artist, the dissector must take care and trouble over the work. It is impossible to learn anatomy from a poor dissection. The artist is not born with the skill to paint and the dissector, likewise, is not born with the skill to dissect. It is care and practice which makes a perfect picture and a perfect dissection.

There are three methods of exposing structures: by ‘sharp’ dissection with the scalpel, by ‘blunt’ dissection with the finger or a similar blunt object, or through the use of scissors. Dissection with scissors involves inserting closed scissors into the area and then using a ‘close and open’ technique to separate tissues. Each technique has merit and careful consideration should be given to where each technique is applied.

It is important to realise that neurovascular structures often run together. Thus, if a nerve is going to a particular place, then it is often accompanied by an artery and a vein. As the vein is usually filled with blood, and is therefore dark in colour, it may be used to identify the location of a neurovascular bundle. It should also be noted that the nerves and blood vessels are like a tree – as they branch away from the centre or trunk, they become smaller. Since dissection, by its very nature, must begin from the outside, the beginner is faced with finding the smallest structures first. This makes early dissection somewhat difficult and emphasises the necessity to apply care to the finding of small but important structures.

A scalpel will sometimes make contact with bone or other hard material and, as a result, will blunt or break. It is necessary, therefore, to sharpen or replace the blade from time to time. An oil-stone is provided in most dissection rooms for the purpose of sharpening the blade on a fixed blade scalpel.

Incisions through the skin should be made with a sharp scalpel and should be deep enough to enter the subcutaneous fatty plane. Note that the skin on the back tends to be thicker than that on the anterior aspect of the trunk and correspondingly more care should be taken with anterior incisions. Once the skin has been incised, by far the best technique is ‘blunt’ dissection with the fingers or with the ‘handle-end’ of the forceps. The skin and subcutaneous fat can often be pared off the underlying structures. In this way, the nerves and blood vessels are easily identified as they emerge through the underlying deep fascia and muscle, en route to the skin.

When removing skin, especially that of the trunk and limbs, the plane of separation between the superficial and deep fascial planes is used. This emphasises an important concept in dissection. The layers of the body, for the most part, are separable from one another and dissection is made correspondingly easier if separation of organs and structures is carried out along anatomical fascial planes.

It is advisable to cut short or shave the hairy parts of the body prior to dissection as it facilitates the dissection of the region.

1.4 CARE OF THE CADAVER

The cadaver is the greatest asset in the study of anatomy and it is necessary, therefore, to preserve and care for it for the duration of the dissection course. The greatest hazard is dehydration and desiccation, usually brought about by air...