Niddah

R. Amram stated: A Tanna taught, 'Its  two thighs are like two silk threads', and in connection with this R. Amram explained: Like those of the woof;  'and its two arms are like two threads of silk', in connection with which R. Amram explained: Like those of the warp. Samuel said to Rab Judah: Shinena,  give no practical decision [on the validity of a birth] unless the embryo has hair [on its head]. But could Samuel have said such a thing, seeing that he ruled, 'In either case must she consider the possibility of a valid birth'? — R. Ammi b. Samuel replied: This was explained to me by the Master Samuel: She must indeed take into consideration the possibility of a valid birth;  but she is not allowed the privilege of the clean days  unless the embryo had hair [on its head]. This then implies that Samuel was doubtful on the point.  But is it not a fact that when a certain sac was submitted to the Master Samuel he said, 'This is forty-one days old', but on calculating the time since the woman had gone to perform her ritual immersion  until that day and finding that there were no more than forty days he declared, 'This man  must have had marital intercourse during her menstrual period' and having been arrested  he confessed?  — Samuel was different from other people because his knowledge was exceptional. IF SHE ABORTED A SANDAL etc. Our Rabbis taught: A sandal is like a sea-fish [of the same name].  At first it is a normal foetus but later it is crushed. R. Simeon b. Gamaliel said: A sandal resembles the tongue of a big ox. In the name of our Masters it was testified: A sandal  must have the facial features.  Rab Judah citing Samuel stated: The halachah is that a sandal  must have the facial features. R. Adda citing R. Joseph who had it from R. Isaac ruled: A sandal  must have the facial features even if only at the back, this being a case similar to that of a man who slapped his fellow and caused his face to turn backwards. In the days of R. Jannai it was desired to declare [the mother of] a sandal that had no facial features as clean.  Said R. Jannai to them: You would declare [the mother of newly born] children  as clean!  — But was it not taught, 'In the name of our Masters it was testified: A sandal  must have the facial features'?  — R. Bibi b. Abaye citing R. Johanan replied: It was on the evidence of R. Nehunya  that this ruling  was learnt.  R. Ze'ira observed: R. Bibi was lucky [to be the first] with his reported traditions, for both I and he were sitting in the presence of R. Johanan when he discoursed upon this tradition, but he  forestalled me and, reporting it first, gained the advantage. Why was a sandal  at all mentioned, seeing that there can be no birth of a sandal without that of an embryo with it?  — If a female child were to be born with it this would be so indeed,  but here we are dealing with one with which a male was born.  As it might have been presumed that, since R. Isaac b. Ammi stated, 'If the woman is first to emit the semen she bears a male child and if the male is first to do it she bears a female child', the one  is a male as well as the other is a male,  hence we were informed [that no such assumption is made, for] it might equally be assumed that both emitted their semen simultaneously so that one might be a male while the other  is a female.  Another explanation:  [Sandal  was mentioned] in order that if a woman bore a female child before sunset and a sandal after sunset  she must count the beginning of her period of menstruation in accordance with the first birth and in accordance with the second birth. As regards the sandal that we learnt