INTRODUCTION. 3 
subsequently lose all trace of such a subdivision. The parts thus repeated are said 
to be serially homologous. But there are other instances of serial homology besides 
those which are manifestly produced by segmentation. The upper limb is serially 
homologous with the lower limb: each is composed of parts which, to a large 
extent, are repeated in the other, and the correct adjustment of this comparison 
between the several parts of the upper and lower limbs constitutes one of the most 
difficult and yet interesting problems of morphology. 
Homoplasy is a term which has been introduced to express a form of corre- 
spondence between organs in different animals which cannot be included under 
the term homology. Two animal groups, which originally have sprung from 
the same stem-form, may independently develop a similar structural character 
which is altogether absent in the ancestor common to both. Thus the common 
ancestor of man and the carnivora in all probability possessed a smooth brain, and 
yet the human brain and the carnivore brain are both richly convoluted. Not 
only this, but certain anatomists seek to reconcile the convolutionary pattern of 
the one with the convolutionary pattern of the other. What correspondence there 
is does not constitute a case of homology, because there is no community of origin, 
but it falls under the term “homoplasy.” Another example is afforded by the 
heart of the mammal and that of the bird. In both of these groups the ventricular 
portion of the heart consists of a right and a left chamber, and yet these chambers 
in the one are not homologous with the corresponding chambers in the other, 
because the common ancestor from which both have sprung possessed a heart with 
a single ventricular cavity, and the double-chambered condition has been a 
subsequent and independent development in the two groups. 
Systematic Anatomy.—The human body is composed of a combination of 
several systems of organs, and the several parts of each system not only present a 
certain similarity in structure, but also fulfil special functions. Thus we have— 
1. The skeletal system, composed of the bones and certain cartilaginous and 
membranous parts associated with them, the study of which is known as osteology. 
2. The articulatory system, which includes the joints or articulations, the study 
of which is termed arthrology. 
3. The muscular system, comprising the muscles, the study of which constitutes 
myology. 
4. The nervous system, in which are included the brain, the spinal cord, the 
spinal and cranial gangha, the sympathetic ganglia, and: the various nerves 
proceeding from and entering these. The study of these parts is expressed by the 
term neurology. In this system the organs of sense may also be included. 
5. The vascular and lymphatic system, including the heart, blood-vessels, the 
lymphatic vessels, and the lymphatic glands. Angeiology is the term applied to the 
study of this system. 
6. The respiratory system, in which we place the lungs, windpipe, and larynx. 
7. The digestive system, which consists of the alimentary canal and its associated 
glands and parts, such as the tongue, teeth, liver, pancreas, ete. 
8. The urogenital system, composed of the urinary organs and the reproductive 
organs—the latter differing in the two sexes. 
The term splanchnology denotes the study of the organs included in the 
respiratory, digestive, and genito-urinary systems. 
9. The integumentary system, consisting of the skin, nails, hair, ete. 
These numerous organs which form the various systems are themselves built up 
of tissues, the ultimate elements of which can only be studied by the aid of the 
microscope. The study of these elements and the manner in which they are 
