GENERAL ANATOMY OF THE MAMMALIAN BODY 
9 
Posterior to the intestinal mass, at the level of the pubic arch, 
may be seen the urinary bladder, especially conspicuous if it 
happens to be distended with urine. If the animal is a male, 
certain of the accessory reproductive organs may be seen as slender 
pointed sacs upon either side in the posterior part of the cavity 
(especially in rodents). If the animal happens to be a female 
in advanced pregnancy, the much enlarged portions of the gravid 
uterus will be pushed up conspicuously into view . 1 
Make an outline drawing of the ventral view of the whole 
specimen , showing the abdominal cavity thus laid open and 
the contained organs in situ, and adding to the drawing as the work 
progresses. 
Cut the pectoralis muscles from their attachment to the ster- 
\ num upon each side and reflect them laterally, thus exposing the 
thoracic wall. 
Open the thoracic cavity by removing with the scissors a wide 
triangular portion of the latero-ventral wall upon each side of the 
midventral line leaving intact the whole line of costal cartilages 
which form the posterior border of the thoracic cavity, the ster¬ 
num, and the diaphragm, the full extent and relations of which 
may now be more clearly seen. Note attached to the inner surface 
of the sternum, the delicate mediastinum, which forms a median 
partition dividing the thoracic cavity into right and left pleural 
cavities. 
Within the space inclosed between the two layers of the medi¬ 
astinum, the heart will be seen enwrapped with its own serous 
membrane, the pericardium. The membrane which lines each 
pleural cavity is the parietal pleura, w T hich is continuous along the 
middorsal and midventral regions with the mediastinal pleura 
of its own side. The lung which lies in each pleural cavity is 
inclosed in the visceral pleura which is a reduplicature of the 
mediastinal pleura dorsal to the heart. 
1 In case there are embryos in the uterus, these should be examined while fresh, 
and their relation to the various extraembryonal parts (see p. 137) noted, after which 
each embryo should be carefully removed with the placenta still attached to it, and 
hardened in some good fixative such as that for which the formula is given on p. 22. 
It may subsequently be preserved to use for the study of the development of 
mammals (p. 137), or, if of suitable size, may be sectioned for the study of the 
general plan of the body (p. 15). 
