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מסכת חולין פרק ד משנה ו

A note on anatomy:  quadrupeds have three bones that descend from pelvis to hoof or foot.  These are, going from the rump to the hoof, the femur, the tibia and the canon bone.  The joint between the femur and tibia, which is analogous to the human knee, is known as the stifle joint, the joint between the tibia and canon bone is known as the hock, and is analogous to the human ankle. 

בהמה שנחתכו רגליה An animal that had its hind-leg severed
מן הארכובה ולמטה

from below the joint (in the gemara there is disagreement as to whether this is the stifle joint or the hock)

כשרה is kosher,
מן הארכובה ולמעלה from the joint and above
פסולה is not kosher (and is considered a treifah),
וכן שנטל צמת הגידים and similarly if the meeting of the sinews was removed.  (This refers to tendons that converge between the hock and stifle joint).
נשבר העצם If the bone was broken (either the tibia, according to those that hold that the joint referred to earlier is the stifle joint, or the cannon bone, according to those that say the joint referred to is the hock)
אם רוב הבשר קים if most of the flesh remains [around the fracture]
שחיטתה מטהרתו its slaughter renders it tahor (and the broken limb is not considered as if it had been severed from the animal while it was still alive which would be tamei)
ואם לאו and if not
אין שחיטתה מטהרתו its slaughter does not render it tahor

משנה ז

השוחט את הבהמה

One who slaughters an animal

ומצא בה שליא

and finds an amniotic sac inside it

נפש היפה תאכל one who is not finicky may eat it,
ואינה מיטמאה

and it does not acquire tumah,

לא טמאת אכלין not the tumah [imparted by] foods (if the placenta subsequently comes into contact with something that is tamei, as it is not considered food),
ולא טמאת נבלות and not the tumah imparted by neveilos (even if the parent was a neveilah).
חשב עליה If he intended [to eat] it,
מטמאה טמאת אוכלין it acquires the tumah of food
אבל לא טמאת נבלות  but not the tumah of neveilos.
שליא שיצתה מקצתה An amniotic sac that partially came out [of its mother]
אסורה באכילה

may not be eaten (for fear that it contained the fetus's head; even if no head is actually found, it may have been dissolved inside the sac);

סימן ולד באישה it is the sign of [the presence of] a fetus by a woman (rendering her tamei, even if no fetus is found)
וסימן ולד בבהמה and it is the sign of a fetus by an animal.
המבכרת שהפילה שליא An animal having its first-born whose amniotic sac aborted,
ישליכנה לכלבים he may throw it to the dogs. (We do not worry about the sanctity of a first-born, as if there had been a fetus inside the sac, it was more likely than not that it would be female or deformed, and thus exempt from sanctity.)
ובמקדשין תיקבר

And in the case of consecrated animals, it must be buried (as even female offspring would be consecrated),

ואין קוברין אותה and we do not bury it
בפרשת דרכים at the crossroads,
ואין תולין אותה באילן and we do not hang it from a tree,
מפני דרכי האמרי because [this is] the superstitions of the Emorites.