20 Fiero Museum or Natura History — Zoé.oey, Vor. XI. 
Ideal section of a Mammal. 
a, Olfactory nerves; b, optic nerve; c, brain; d, ear conch or pinna; e, epiglottis; f, cesophagus; g, 
thyroid glands; h, vertebral column or back-bone; i, spinal cord; j, trachea; k, lungs; 1, heart; m, 
diaphram; n, liver; 0, pancreas; p, stomach; q, spleen; r, kidney; s, intestines; t, bladder; u, scrotum 
and testes; v, anus. (After Owen.) 
The Heart — The heart in all mammals is divided into four chambers 
known as auricles and ventricles, but the shape is more or less 
variable in different forms. Each auricle communicates with the 
ventricle of the same side, the opening being provided with valves 
which permit the blood to pass only in the right direction, viz., from 
the auricle to the ventricle. Briefly stated, the circulation of the 
blood is accomplished as follows: It enters the right auricle, which 
is supplied by means of the vene cave, and thence to the ventricle 
of the same side, from whence it is forced into the lungs through 
the pulmonary artery and there absorbs the necessary oxygen and 
is relieved of carbon dioxide. From the lungs by means of the 
pulmonary veins it enters the left auricle and passes through the 
left ventricle into the aorta, passing out again through the large 
arteries (such as the ‘‘carotid”’ and “‘brachial’’), which arise from 
it, and thence into the general system, where, after passing through 
the capillaries, it is conducted by a diversity of veins to the large 
superior and inferior venee cavee and thence back again to the right 
auricle. 
There is considerable variation in mammals in the mode in 
which different arteries arise from the aorta. In most cases the 
right brachial and right carotid have a common origin known as 
the innominate artery in human anatomy. The other two may 
extend from this, as in the Ungulates, or may arise separately from 
the aorta, as in Man, or as is common in many species, the left 
carotid may arise from the “innominate” and the left brachial 
