cord and brain. The Lesson on the larynx is from its very nature disconnected from the others. The tissues of reproduction naturally form the subject of the concluding Lesson.

I have called it an Elementary Course because my class is divided into an Elementary and an Advanced Division, and this work is intended for the former only. I have found it, however, practically convenient to go into some subjects fully in the Elementary Class and to leave certain other subjects entirely for the advanced class. Thus while, on the

one hand, some topics seem to be treated here in a more than elementary manner; others, on the other hand, e.g. the ear and hearing, binocular vision, &c., are entirely absent, being reserved for the advanced class.

I presuppose the student to have gone through a course of Elementary Biology, in which he has worked out the Lessons of Prof. Huxley and Dr Martin. He will thus have acquired a knowledge of the fundamental principles of Histology and Physiology, know how to use his microscope and possess a good acquaintance with the Anatomy of the Frog. The dissection of the dog and the rabbit as directed in Lesson I., in which attention is paid only to details of physiological importance, will at once put him in a position for the study of Physiology, strictly so called.

The instructions given are generally complete in themselves; but the student should have access to the Handbook of the Physiological Laboratory, to which (under the abbreviation Hdb.) he is frequently referred.

The demonstrations, appended to each Lesson illustrate the lecture belonging to the Lesson, and are for the most

part observations or experiments too difficult for the student to carry out for himself. A list of them is given merely in order that the student may know what he has to see. Nothing therefore is said about the manner of executing them; I may, however, remark that none of them are painful, since they are of such a nature that anesthetics where necessary can always be used.

The work marked out occupies my class the whole of two terms, i.e. from fifteen to eighteen weeks, the lectures being delivered twice weekly, and the practical work being carried on immediately after the lecture as well as on the intermediate days. The plan of work, in fact, closely follows that of Prof. Huxley in his Elementary Biology. It is, of course, not necessary that all the details of each chapter should be worked over by each student. Practical work of this kind is only of value in so far as it suggests or corrects ideas. The student who has mounted an exquisitely thin and beautifully stained section, is only just so much the worse for his pains (as far as physiology is concerned), if he does not understand what the section means. Hence, when the features of some of the fundamental tissues and the general working of the more important mechanisms have been really learnt, and the student has got, by doing things for himself, to know the value of a physiological experiment and the pitfalls that are hidden under carmine and Canada balsam, he may be safely trusted to fill in the details of his study by means of reference to mounted specimens and to mere demonstrations or even to descriptions of experiments. How much practical work is needed by each student must depend on a variety of

circumstances; and the choice of subjects studied in detail ought to be varied from time to time. In the Lessons, therefore, selection has been exercised to a very limited extent, and most of the topics have been treated with equal fulness.

In no case whatever are the directions given intended to be exhaustive. In the use of reagents, in the details of the microscopical work, and in the various experiments, the counsels given are those which have, on the whole, been found most useful for students in the laboratory. They are not in any way to be considered as forming a practical treatise on Histology or Physiology. That ground is already occupied by the Handbook for the Physiological Laboratory, to which the present little book may be looked upon as an introduction.

So much of the labour of preparing this volume for the press has fallen on my able Demonstrator, Mr J. N. LANGLEY, B.A., of St John's College, that his name naturally appears on the title-page as well as my own. To Prof. Huxley and to Dr H. N. Martin I am indebted for much valuable advice.

TRINITY COLLEGE, CAMBRIDGE,
May, 1876.

M. FOSTER.

LESSON I.

DISSECTION OF A RABBIT AND OF A DOG.

'A. 1. Make a median incision through the skin, down the whole length of the front of the body from the neck to the pubis, and reflect the skin as far as possible on both sides.

Observe the thin, pale, abdominal muscles. These, in the rabbit, are indistinct and need not be specially studied.

In the Dog observe

a. The tendinous aponeuroses of the abdominal muscles forming in the middle line the white linea alba.

b.

The externus obliquus abdominis, a thin muscle, with
descending fibres, stretching from the ribs above and
from the back to the linea alba and the pubis.

C. The recti abdominis, one on either side of the middle
line, covered by the tendon of the externus obliquus.
Ifb be carefully reflected, there will be seen underneath:
d. The internus obliquus abdominis, with ascending fibres;
and underneath the upper part of this

1 N. B. A and B should be carried out on the first day, in order that the viscera may be useful for microscopic observation, and the brain in good condition. If for any reason the dissection be delayed beyond the first day, the sections which are marked with an asterisk should be omitted.